Power Conversion from Milliamps to Amps at Ultra-High Efficiency

AN54-1

Application Note 54

March 1993

Power Conversion from Milliamps to Amps at Ultra-HighEfficiency (Up to 95%)

and LTC are registered trademarks and LT is a trademark of Linear Technology Corporation.Burst Mode is a trademark of Linear Technology Corporation.

Dimitry Goder

Randy Flatness

INTRODUCTION

High efficiency is frequently the main goal for powersupplies in portable computers and hand-held equipment.Efficient converters are necessary in these applications tominimize power drain on the input source (batteries, etc.)and heat buildup in the power components, allowing forsmaller, lighter, and longer-lived systems. Power conver-sion efficiency must be in the 90% range in order to meetthese goals. This application note features power supplycircuits that satisfy these design requirements and attainhigh efficiency over a wide operating range.

The recent development of the LTC®1142, LTC1143,LTC1147, LTC1148, and LTC1149 makes ultra-high effi-ciency conversion possible. In addition, the LTC1148,LTC1149, and LTC1142 are synchronous switching regu-lators, achieving high efficiency conversion at outputcurrents in excess of 10A. These controllers feature a

current mode architecture that has automatic BurstModeTM operation at low currents. This technology makes90% efficiencies possible at output currents as low as10mA, maximizing battery life while a product is in sleepor standby mode.

These ultra-high efficiency converters also implementconstant off-time architecture, fully synchronous switch-ing and low dropout regulation. All these features makethis series of converters a really excellent choice for a vastvariety of applications.

Achieving high efficiency is one of the primary goals ofswitching regulator design. Every application circuit shownin this note includes detailed efficiency graphs. Almost all ofthe magnetic parts used in the circuits are standard prod-ucts, available off-the-shelf from various manufacturers.

Application Note 54

AN54-2

TABLE OF CONTENTSBuckLTC1148: (5V-14V to 5V/1A) Buck Converter with Surface Mount Technology ................................................................ Figure 1 AN54-3LTC1148: (5V-14V to 5V/2A) Buck Converter .................................................................................................................. Figure 2 AN54-4LTC1148: (5V-14V to 5V/2A) High Frequency Buck Converter with Surface Mount Technology...................................... Figure 3 AN54-5LTC1148: (4V-14V to 3.3V/1A) Buck Converter with Surface Mount Technology ............................................................. Figure 4 AN54-6LTC1148: (4V-14V to 3.3V/2A) Buck Converter with Surface Mount Technology ............................................................. Figure 5 AN54-7LTC1148: (5V to 3.3V/5A) High Efficiency Step-Down Converter ..................................................................................... Figure 6 AN54-8LTC1148: (5V to 3.5V/3A) High Efficiency Step-Down Converter .................................................................................... Figure 7 AN54-9LTC1149: (10V-48V to 5V/2A) High Voltage Buck Converter ........................................................................................... Figure 8 AN54-10LTC1149: (10V-48V to 5V/2A) High Voltage Buck Converter with Large P-Channel and N-Channel MOSFETs ................ Figure 9 AN54-11LTC1149: (10V-48V to 3.3V/2A) High Voltage Buck Converter ....................................................................................... Figure 10 AN54-12LTC1149: (10V-48V to 12V/2A) High Voltage Buck Converter ........................................................................................ Figure 11 AN54-13LTC1149: (16VRMS to 13.8/10A) Buck Converter ........................................................................................................... Figure 12 AN54-14LTC1149: (32VRMS to 27.6V/5A) Buck Converter ........................................................................................................... Figure 13 AN54-15LTC1147: (5V-14V to 5V/1A) Buck Converter with Surface Mount Technology .............................................................. Figure 14 AN54-16LTC1147: (4V-14V to 3.3V/1A) Buck Converter with Surface Mount Technology ........................................................... Figure 15 AN54-17LTC1147: (4V-8V to 3.3V/1.5A) Buck Converter with Surface Mount Technology .......................................................... Figure 16 AN54-18LTC1148: (10V-14V to 5V/10A) High Current Buck Convert .......................................................................................... Figure 17 AN54-19LTC1149: (12V-36V to 5V/5A) High Current, High Voltage Buck Converter ................................................................... Figure 18 AN54-20LTC1149: (12V-48V to 5V/10A) High Current, High Voltage Buck Converter ................................................................. Figure 19 AN54-21LTC1149: (32V-48V to 24V/10A) High Current, High Voltage Buck Converter ............................................................... Figure 20 AN54-22LTC1143: (5.2V-14V to 3.3V/2A and 5V/2A) Dual Buck Converter ................................................................................ Figure 26 AN54-28LTC1148HV-5: (5.2V-18V to 5V/1A) High Voltage Buck Converter ................................................................................ Figure 27 AN54-29LTC1148HV-3.3 (4V-18V to 3.3V/1A) High Voltage Buck Converter .............................................................................. Figure 28 AN54-30LTC1148HV: (12.5V-18V to 12V/2A) High Voltage Buck Converter ............................................................................... Figure 29 AN54-31LTC1142: (6.5V-14V to 3.3V/2A, 5V/2A, 12V/0.15A) Triple Output Buck Converter ...................................................... Figure 30 AN54-32LTC1142HV: (6.5V-18V to 3.3V/2A, 5V/2A, 12V/0.15A) High Voltage Triple Output Buck Converter ............................ Figure 31 AN54-34Single LTC1149: Dual Output Buck Converter ............................................................................................................... Figure 35 AN54-38LTC1148: (8V-15V to 5V/2A) Constant Frequency Buck Converter ................................................................................ Figure 36 AN54-39LTC1148: (4.5V-6.5V to 3.3V/2A) Constant Frequency Buck Converter ......................................................................... Figure 37 AN54-40

Buck-Boost and Inverting TopologiesLTC1148: (4V-14V to 5V/1A) SEPIC Converter .............................................................................................................. Figure 21 AN54-23LTC1148: (4V-14V to 5V/0.5A, – 5V/0.5A) Split Supply Converter ................................................................................. Figure 22 AN54-24LTC1148: (4V-10V to – 5V/1A) Positive-to-Negative Converter ...................................................................................... Figure 23 AN54-25LTC1148: (5V-12V to –15V/0.5A) Buck-Boost Converter .............................................................................................. Figure 24 AN54-26

BoostLTC1148: (2V-5V to 5V/1A) Boost Converter ................................................................................................................. Figure 25 AN54-27

Battery Charging CircuitsLTC1148: High Efficiency Charger Circuit ...................................................................................................................... Figure 32 AN54-35LTC1148: High Voltage Charger Circuit ......................................................................................................................... Figure 33 AN54-36LTC1142A: High Efficiency Power Supply Providing 3.3V/2A with Built-In Battery Charger ......................................... Figure 34 AN54-37

Appendix ATopics of Common Interest ........................................................................................................................................................... AN54-40

Appendix BSuggested Manufacturers ............................................................................................................................................................. AN54-42

AN54-3

Application Note 54

LTC1148: (5V-14V to 5V/1A) Buck Converter withSurface Mount Technology

A basic LTC1148 application is shown in Figure 1A. This isa conventional step-down converter that provides 5V out-put at 1A maximum output current. All the componentsused are surface mounted and no heat sink is required.During Q1 on-time, inductor L1's current is sensed by R2and monitored by an internal current sensing comparator.To filter out noise from the current sense waveform, C6 isadded to the circuit. When the current ramp reaches apreset value, Q1 is turned off, and a clamp diode D1 startsconducting for a short period of time, until the internalcontrol logic senses that Q1 is completely off. ThenNDRIVE output goes high turning Q2 on, which shorts outD1. This provides synchronous rectification and signifi-cantly reduces conduction losses during Q1’s off-time.

This regulator has a constant off-time defined by the timingcapacitor C5. To control the output, on-time is varied,

changing the operating frequency and therefore, the dutycycle. If the input voltage is reduced, frequency decreaseskeeping output voltage at the same level. Q1’s on-timestretches to infinity with low input voltage, providing 100%duty cycle and very low dropout. Under dropout condi-tions, the output voltage follows the input, less any resis-tive losses in Q1, L1 and R2.

Under conditions of light output currents, the regulatorenters Burst Mode operation to ensure high efficiency.Continuous operation is interrupted by an internal voltagesensing comparator with built-in hysteresis. in this modeboth Q1 and Q2 are turned off and the comparator monitorsdecreasing output voltage. When the output capacitordischarges below a fixed threshold, operation resumes fora short period of time bringing the output voltage back tonormal. Then the regulator shuts down again conservingquiescent current. Under Burst Mode operation the outputripple is typically 50mV as set by the hysteresis in thecomparator.

Kool Mµ is a registered trademark of Magnetics, Inc.

Figure 1A. LTC1148: (5V-14V to 5V/1A) Buck Converter with Surface Mount Technology

AN54 • F01AC1 (Ta) C3 AVX (Ta) TPSD226K025R0200 ESR = 0.200Ω IRMS = 0.775A C7 AVX (Ta) TPSE227K010R0080 ESR = 0.080Ω IRMS = 1.285A Q1 SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC Q2 SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC D1 MOTOROLA SCHOTTKY VBR = 40V

ITH

CT

SGND PGND

LTC1148-5

VINPDRIVE

SENSE +

SENSE –

NDRIVE

+

C6 0.01µF

+

VIN 5V TO 14V

C1 1µF

R1 1k

C4 3300pF X7R

C5 390pF NPO

10

4

1

8

7

14

Q1 Si9430DY

Q2 Si9410DY

D1 MBRS140T3

C3 22µF × 2 25V

100µH

R2 0.1Ω

5V 1A

C7 220µF 10V

3

11

12

SHUTDOWN

6

C2 0.1µF

+

L1

1

2

4

3

R2 KRL SP-1/2-A1-0R100J Pd = 0.75W L1 COILTRONICS CTX100-4 DCR = 0.175Ω Kool Mµ® CORE

ALL OTHER CAPACITORS ARE CERAMIC

QUIESCENT CURRENT = 180µA TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 200mA

Application Note 54

AN54-4

Figure 1B shows efficiency versus output current for threedifferent input voltages. Generally speaking, efficiencydrops as a function of input voltage due to gate chargelosses and LTC1148 DC bias current. The curves convergeat maximum output current as these losses become lesssignificant.

OUTPUT CURRENT (A)0.001

50

EFFI

CIEN

CY (%

)

70

80

90

100

0.01 0.1 1

AN54 • F01B

60

VIN = 6V

VIN = 10V

VIN = 14V

Figure 1B. LTC1148: (5V-14V to 5V/1A) Buck ConverterMeasured Efficiency

Figure 2A. LTC1148: (5V-14V to 5V/2A) Buck Converter

AN54 • F02A

C1 (Ta) C3 AVX (Ta) TPSD226K025R0200 ESR = 0.200Ω IRMS = 0.775A C7 AVX (Ta) TPSE227K010R0080 ESR = 0.080Ω IRMS = 1.285A Q1 SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC Q2 SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC D1 MOTOROLA SCHOTTKY VBR = 40V R2 KRL SL- 1-C1-0R050J Pd = 1W L1 COILTRONICS CTX62-2-MP DCR = 0.040Ω MPP CORE (THROUGH HOLE)


ITH

CT

LTC1148-5

VIN

SENSE +

SENSE –

+

C6 0.01µF

+

VIN 5V TO 14V C1

1µF

R1 1k

C4 3300pF X7R

C5 470pF NPO

10

4

1

8

7

14

Q1 Si9430DY

Q2 Si9410DY

D1 MBRS140T3

C3 22µF × 3 25V

L1 62µH

R2 0.05Ω

5V 2A

C7 220µF × 2 10V


3

11

12

SHUTDOWN

6

C2 0.1µF

+

SGND PGND

PDRIVE

NDRIVE

LTC1148: (5V-14V to 5V/2A) Buck Converter

A step-down regulator with 2A output current capability isshown in Figure 2A. To provide higher output power levelsthe sense resistor value is decreased, thus increasing thecurrent limit. This also increases maximum allowableripple current in the inductor, so its value can be reduced.Note that timing capacitor C5 is changed to optimizeperformance for a standard inductor value. In this FigureC7 consists of two parallel capacitors ensuring minimumcapacitance requirement for all conditions. A circuit boardhas been laid out for this circuit and has subsequentlybeen thoroughly tested under full operating conditionsand optimized for mass production requirements. A Ger-ber file for the board is available upon request.

AN54-5

Application Note 54


50

EFFI

CIEN

CY (%

)

70

80

90

100

0.01 0.1 2

AN54 • F02B

60

VIN = 6V

VIN = 10V

VIN = 14V

1

Figure 2B. LTC1148: (5V-14V to 5V/2A) Buck ConverterMeasured Efficiency

LTC1148: (5V-14V to 5V/2A) High Frequency BuckConverter with Surface Mount Technology

Figure 3A presents essentially the same circuit as Figure2A, but implementing changes to operate at a higherfrequency. Timing capacitor C5 is reduced to achievehigher switching rate. This approach allows the use of asmaller value inductor with surface mount technology,resulting in a more compact design.

C1 (Ta) C3 AVX (Ta) TPSD226K025R0200 ESR = 0.200Ω IRMS = 0.775A C7 AVX (Ta) TPSE227K010R0080 ESR = 0.080Ω IRMS = 1.285A Q1 SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC Q2 SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC D1 MOTOROLA SCHOTTKY VBR = 40V R2 KRL SL-1-C1-0R050J Pd = 1W L1 COILTRONICS CTX33-4 DCR = 0.06Ω Kool Mµ CORE


ITH

CT

LTC1148-5

VIN

SENSE +

SENSE –

+

C6 0.01µF

+

VIN 5V TO 14V

C1 1µF

R1 1k

C4 3300pF X7R

C5 220pF NPO

10

4

1

8

7

14

Q1 Si9430DY

Q2 Si9410DY

D1 MBRS140T3

C3 22µF × 3 25V

33µH

R2 0.05Ω

5V 2A

C7 220µF × 2 10V


3

11

12

SHUTDOWN

6

C2 0.1µF

+

L1

1

2

4

3

AN54 • F03A

SGND PGND

PDRIVE

NDRIVE

Figure 3A. LTC1148: (5V-14V to 5V/2A) High Frequency Buck Converter with Surface Mount Technology

Application Note 54

AN54-6

Figure 4A. LTC1148: (4V-14V to 3.3V/1A) Buck Converter with Surface Mount Technology

Let us compare efficiency graphs in Figures 2B and 3B.Gate charge losses are directly proportional to operatingfrequency, and as a result the efficiency of Figure 3A is

decreased. However, the effect is most noticeable at highinput voltages and low currents. At maximum load I2Rlosses dominate so that the regulator performance variesonly slightly. These two circuits illustrate the fact that bestoverall efficiency is reached at moderate frequencies. Theyrepresent a nice example of compromising between regu-lator compactness and efficiency.

AN54 • F04A

C1 (Ta) C3 AVX (Ta) TPSD226K025R0200 ESR = 0.200Ω IRMS = 0.775A C7 AVX (Ta) TPSE227K010R0080 ESR = 0.080Ω IRMS = 1.285A Q1 SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC Q2 SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC D1 MOTOROLA SCHOTTKY VBR = 40V R2 KRL SP-1/2-A1-0R100J Pd = 0.75W L1 COILTRONICS CTX100-4 DCR = 0.175Ω Kool Mµ CORE ALL OTHER CAPACITORS ARE CERAMIC

ITH

CT

LTC1148-3.3

VIN

SENSE +

SENSE –

+

C6 0.01µF

+

VIN 4V TO 14V C1

1µF

R1 1k

C4 3300pF X7R

C5 560pF NPO

10

4

1

8

7

14

Q1 Si9430DY

Q2 Si9410DY

D1 MBRS140T3

C3 22µF × 2 25V

100µH

R2 0.1Ω

3.3V 1A

C7 220µF 10V


3

11

12

SHUTDOWN

6

C2 0.1µF

+

L1

1

2

4

3

SGND PGND

PDRIVE

NDRIVE


50

EFFI

CIEN

CY (%

)

70

80

90

100

0.01 0.1 1

AN54 • F03B

60

VIN = 6V

VIN = 10V

VIN = 14V

2

Figure 3B. LTC1148: (5V-14V to 5V/2A) High FrequencyBuck Converter Measured Efficiency

LTC1148: (4V-14V to 3.3V) Buck Converters withSurface Mount Technology

Figures 4A and 5A show application circuits for theLTC1148-3.3 which provides a fixed 3.3V output. Thecircuits deliver 1A and 2A output currents, and use exactlythe same circuit configuration and component values asFigures 1A and 2A. Even though the LTC1148 can achievelow dropout, the minimum input voltage is limited to 4V tomeet requirements for power MOSFET gate drive, and toensure proper operation of the LTC1148 internal circuitry.

AN54-7

Application Note 54

Low output voltage causes efficiency degradation at lightloads when the chip’s DC supply current and gate chargecurrent play major parts in total losses. Figures 4B and


5B illustrate this point as the efficiency falls off below10mA output current. High input voltage compounds theproblem.

Figure 4B. LTC1148: (4V-14V to 3.3V/1A) Buck ConverterMeasured Efficiency


50

EFFI

CIEN

CY (%

)

70

80

90

100

0.01 0.1 1

AN54 • F04B

60

VIN = 5V

VIN = 10V

VIN = 14V


50

EFFI

CIEN

CY (%

)

70

80

90

100

0.01 0.1 2

AN54 • F05B

60

1

VIN = 5V

VIN = 10V

VIN = 14V

Figure 5B. LTC1148: (4V-14V to 3.3V/2A) Buck ConverterMeasured Efficiency

AN54 • F05A

C1 (Ta) C3 AVX (Ta) TPSD226K025R0200 ESR = 0.200Ω IRMS = 0.775A C7 AVX (Ta) TPSE227K010R0080 ESR = 0.080Ω IRMS = 1.285A Q1 SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC Q2 SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC D1 MOTOROLA SCHOTTKY VBR = 40V R2 KRL SL-1-C1-0R050J Pd = 1W L1 COILTRONICS CTX50-2-MP DCR = 0.032Ω MPP CORE (THROUGH HOLE)


ITH

CT

LTC1148-3.3

VIN

SENSE +

SENSE –

+

C6 0.01µF

+

VIN 4V TO 14V C1

1µF

R1 1k

C4 3300pF X7R

C5 470pF NPO

10

4

1

8

7

14

Q1 Si9430DY

Q2 Si9410DY

D1 MBRS140T3

C3 22µF × 3 25V

L1 50µH

R2 0.05Ω

3.3V 2A

C7 220µF × 2 10V


3

11

12

SHUTDOWN

6

C2 0.1µF

+

SGND PGND

PDRIVE

NDRIVE

Application Note 54

AN54-8

LTC1148: (5V to 3.3V/5A) High EfficiencyStep-Down Converter

Many new microprocessor designs require 3.3V, yet theyare used in systems where 5V is the primary source ofpower. A high efficiency 5V to 3.3V converter is drawn inFigure 6A. It supplies up to 5A load using only surfacemount components. Two P-channel MOSFETs are con-nected in parallel to decrease their conduction losses.Efficiency at 5V input is 90%; this means only 1.6W is lost.The lost power is distributed between RSENSE, L1 and thepower MOSFETs, thus no heat sinking is required. OUTPUT CURRENT (A)

EFFI

CIEN

CY (%

)

100

90

80

700.001 0.1 1 10

AN54 • F06B

0.01

Figure 6B. LTC1148: (5V to 3.3V/5A)Buck Converter Measured Efficiency

Figure 6A. LTC1148: (5V to 3.3V/5A) High Efficiency Step-Down Converter

0V = NORMAL >2V = SHUTDOWN

Q1 Si9433DY

Q2 Si9433DY

+ C1 1µF

C2 0.1µF

C7 0.01µF

L1 5µH

R2 0.02Ω

VOUT 3.3V 5A

+

VIN 5V

C5 150pF NPO

C4 3300pF

R1 470Ω + C6

220µF 10V × 3

C3 33µF 6.3V × 2

D1 MBRS140T3

AN54 • F06A

Q3 Si9410DY

ITH

CT

SGND PGND

LTC1148-3.3

VINPDRIVE

SENSE +

SENSE –

NDRIVE

SHUTDOWN10

4

1

8

7

14

3

11

12

6

C1 TANTALUM C3 PANASONIC ECG-COJB330 C6 AVX (Ta) TPSE227K01R0080 ESR = 0.080Ω IRMS = 1.285A Q1, Q2 SILICONIX PMOS BVDSS = 12V DCRON = 0.075Ω Qg = 60nC Q3 SILICONIX NMOS BVDSS = 30V DCRON = 0.050Ω Qg = 30nC D1 MOTOROLA SCHOTTKY VBR = 30V R2 KRL MP-2A-C1-0R020J Pd = 3W L1 COILTRONICS CTX02-12483-1

AN54-9

Application Note 54

LTC1148: (5V to 3.5V/3A) High EfficiencyStep-Down Converter

Some processors require 3.5V or other intermediate volt-age derived from a 5V supply. A good solution for them isthe circuit in Figure 7A. An adjustable version of theLTC1148 allows precise output voltage adjustment, whilepreserving efficiencies of 95%. The output voltage is setby resistors R3 and R4.


EFFI

CIEN

CY (%

)

100

95

90

85

80

75

70

65

600.01 0.1

AN54 • F07B

1 4

Figure 7B. LTC1148: (5V to 3.5V/3A)Measured Efficiency

Q1 Si9433DY

AN54• F07A

C6, 0.01µF

C2 0.1µF

VOUT 3.5V 3A

SHUTDOWN100pF

C6 100µF 10V × 3

C3 22µF 25V × 2

R4 10k 1%

L1 10µH

LTC1148

+

C4 3300pF

X7R

1

2

3

4

5

6

7

14

13

12

11

10

9

8

PDRIVE

NC

VIN

CT

INT VCC

ITH

SENSE–

NDRIVE

NC

PGND

SGND

SHUTDOWN

ADJ

SENSE+

C3 AVX (Ta) TPSD226M025R0200 ESR = 0.20Ω IRMS = 0.866A C6 AVX (Ta) TPSD107M01R0100 ESR = 0.10Ω IRMS = 1.225A Q1 SILICONIX PMOS BVDSS = 12V DCRON = 0.110Ω Qg = 20nC Q2 SILICONIX NMOS BVDSS = 30V DCRON = 0.05Ω Qg = 30nC D1 MOTOROLA SCHOTTKY VBR = 30V R2 KRL SL-C1-1/2-0R033J Pd = 1/2W L1 COILTRONICS CTX10-4 DCR = 0.038Ω Kool Mµ CORE

+

R3 18.2k 1%

R2 0.033Ω

D1 MBRS130T3

R1 510Ω

Q2 Si9410DY

VOUT = 1.25V (1 + R3/R4)

+

VIN 5V+

C5 180pF

NPO

Figure 7A. LTC1148: (5V to 3.5V/3A) High Efficiency Step-Down Converter

Application Note 54

AN54-10

LTC1149: (10V-48V to 5V/2A) High VoltageBuck Converter

Previous circuits can accept inputs up to 14V. If higherinput voltage is required the LTC1149 can be used. This ICis designed for inputs of up to 48V. A basic step-downapplication circuit is shown in Figure 8A. It operates in thesame fashion as the circuit in Figure 1A and provides5V/2A output. However, different MOSFETs are used sincethey must withstand 48V between source and drain. Highcurrent efficiency exceeds 92% over wide range of inputvoltages. Since the control and drive circuitry are powereddirectly from the input line, DC bias current and gatecharge current result in slightly lower efficiency at lightand moderate loads due to high input voltage (relative toLTC1148). This characteristic is eliminated in the circuit ofFigure 11A. A circuit board has been laid out for this circuitand has subsequently been thoroughly tested under full

operating conditions and optimized for mass productionrequirements. A Gerber file for the board is available uponrequest.


50

EFFI

CIEN

CY (%

)

70

80

90

100

0.01 0.1 2

AN54 • F08B

60

1

VIN = 12V

VIN = 48V

VIN = 36V

VIN = 24V

Figure 8B. LTC1149: (10V-48V to 5V/2A) High VoltageBuck Converter Measured Efficiency

AN54 • F08A

C2 UNITED CHEMI-CON (Al) LXF63VB331M12.5 x 30 ESR = 0.170Ω IRMS = 1.280A C4 (Ta) C10 SANYO (OS-CON) 10SA22OM ESR = 0.035Ω IRMS = 2.360A Q1 IR PMOS BVDSS = 60V RDSON = 0.280Ω CRSS = 65pF Qg = 19nC Q2 IR NMOS BVDSS = 60V RDSON = 0.100Ω CRSS = 79pF Qg = 28nC D1 SILICON VBR = 75V D2 MOTOROLA SCHOTTKY VBR = 60V R2 KRL NP-1A-C1-0R050J Pd = 1W L1 COILTRONICS CTX62-2-MP DCR = 0.040Ω MPP CORE


VCC

VCC

CAP

SD1

SD2

ITH

CT

LTC1149-5

PGATE

VIN

SENSE +

SENSE –

NGATE

D1 1N4148

+

C9 0.01µF

+

VIN 10V TO 48V C1

0.1µF

+ C4 1µF

C5 0.1µF

C6 0.068µF

Z5U

R1 1k

C7 3300pF X7R

C8 680pF NPO

3

5

16 10

15

7

6

1 4

9

8

13

C3 0.047µF Z5U

Q1 IRFU9024

Q2 IRFU024

D2 MBR160

C2 330µF 63V

L1 62µH

R2 0.05Ω

5V 2A

C10 220µF × 2 10V

QUIESCENT CURRENT = 1.5mA TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 570mA

2

11

12

14

SGND PGND

PDRIVE

RGND

Figure 8A. LTC1149: (10V-48V to 5V/2A) High Voltage Buck Converter

AN54-11

Application Note 54

LTC1149: (10V-48V to 5V/2A) High Voltage BuckConverter with Large P-Channel and N-ChannelMOSFETs

Figure 9A is similar to Figure 8A with much larger MOSFETs(TO220 package). These transistors have lower RDS(ON)which reduces their I2R losses by roughly a factor of 2.However, the efficiency improves (compared to Figure8B) only at 2A output current with minimum input voltage.Under other conditions higher gate capacitance causesincreased gate charge current leading to higher driverloss. Also for high input voltages (roughly greater than24V), transition losses play a significant part. These lossesare proportional to the reverse transfer capacitance CRSS,maximum output current, and the square of input voltage.Larger CRSS for the oversized P-channel MOSFET causesan efficiency drop (especially for higher input voltages).

Remember, the “best” MOSFET selection depends on theparticular application.

Figure 9B. LTC1149: (10V-48V to 5V/2A) Measured Efficiencywith Large P-Channel and N-Channel MOSFETs


50

EFFI

CIEN

CY (%

)

70

80

90

100

0.01 0.1 2

AN54 • F09B

60

1

VIN = 12V

VIN = 48V

VIN = 24V

VIN = 36V

AN54 • F09A

C2 UNITED CHEMI-CON (Al) LXF63VB331M12.5 x 30 ESR = 0.170Ω IRMS = 1.280A C4 (Ta) C10 SANYO (OS-CON) 10SA220M ESR = 0.035Ω IRMS = 2.360A Q1 IR PMOS BVDSS = 60V RDSON = 0.140Ω CRSS = 100pF Qg = 34nC Q2 IR NMOS BVDSS = 60V RDSON = 0.050Ω CRSS = 100pF Qg = 32nC D1 SILICON VBR = 75V D2 MOTOROLA SCHOTTKY VBR = 60V R2 KRL NP-1A-C1-0R050J Pd = 1W L1 COILTRONICS CTX62-2-MP DCR = 0.040Ω MPP CORE ALL OTHER CAPACITORS ARE CERAMIC

VCC

VCC

CAP

SD1

SD2

ITH

CT

LTC1149-5

VIN

SENSE +

SENSE –

D1 1N4148

+

C9 0.01µF

+

VIN 10V TO 48V

C1 0.1µF

+ C4 1µF

R1 1k

C7 3300pF X7R

C8 680pF NPO

3

5

16 10

15

7

6

1 4

9

8

13

C3 0.047µF Z5U

Q1 IRF9Z34

Q2 IRFZ34

D2 MBR160

C2 330µF 63V

L1 62µH

R2 0.05Ω

5V 2A

C10 220µF × 2 10V


2

11

12

14

PGATE

NGATESGND PGND

PDRIVE

RGND

C5 0.1µF

C6 0.068µF

Z5U

Figure 9A. LTC1149: (10V-48V to 5V/2A) High Voltage Buck Converter with Large P-Channel and N-Channel MOSFETs

Application Note 54

AN54-12

LTC1149: (10V-48V to 3.3V/2A) High VoltageBuck Converter

If 3.3V has to be generated efficiently from a high voltageinput, use the circuit of Figure 10A. It copies the configu-ration presented in Figure 8A but uses the LTC1149-3.3regulator to provide a precise 3.3V output. In spite ofthe high input and low output voltages, efficiency stillreaches 92%.


50

EFFI

CIEN

CY (%

)

70

80

90

100

0.01 0.1 2

AN54 • F10B

60

1

VIN = 48V

VIN = 12V

VIN = 36V

VIN = 24V

Figure 10B. LTC1149: (10V-48V to 3.3V/2A) High VoltageBuck Converter Measured Efficiency

Figure 10A. LTC1149: (10V-48V to 3.3V/2A) High Voltage Buck Converter

AN54 • F10A

C2 UNITED CHEMI-CON (Al) LXF63VB331M12.5 × 30 ESR = 0.170Ω IRMS = 1.280A C4 (Ta) C10 SANYO (OS-CON) 10SA220M ESR = 0.035Ω IRMS = 2.360A Q1 IR PMOS BVDSS = 60V RDSON = 0.280Ω CRSS = 65pF Qg = 19nC Q2 IR NMOS BVDSS = 60V RDSON = 0.100Ω CRSS = 79pF Qg = 28nC D1 SILICON VBR = 75V D2 MOTOROLA SCHOTTKY VBR = 60V R2 KRL NP-1A-C1-0R050J Pd = 1W L1 COILTRONICS CTX50-2-MP DCR = 0.032Ω MPP CORE


VCC

VCC

CAP

SD1

SD2

ITH

CT

LTC1149-3.3

VIN

SENSE +

SENSE –

D1 1N4148

+

C9 0.01µF

+

VIN 10V TO 48V C1

0.1µF

+ C4 1µF

C5 0.1µF

C6 0.068µF

Z5U

R1 1k

C7 3300pF X7R

C8 470pF NPO

3

5

16 10

15

7

6

1 4

9

8

13

C3 0.047µF Z5U

Q1 IRFU9024

Q2 IRFU024

D2 MBR160

C2 330µF 63V

L1 50µH

R2 0.05Ω

3.3V 2A

C10 220µF 10V


2

11

12

14

PGATE

NGATESGND PGND

PDRIVE

RGND

AN54-13

Application Note 54

AN54 • F11A

C2 UNITED CHEMI-CON (Al) LXF63VB331M12.5 × 30 ESR = 0.170Ω IRMS = 1.280A C4 (Ta) C10 SANYO (OS-CON) 10SA220M ESR = 0.035Ω IRMS = 2.360A Q1 IR PMOS BVDSS = 60V RDSON = 0.140Ω CRSS = 100pF Qg = 34nC Q2 IR NMOS BVDSS = 60V RDSON = 0.050Ω CRSS = 100pF Qg = 32nC D1 SILICON VBR = 75V D2 MOTOROLA SCHOTTKY VBR = 60V R2 KRL NP-1A-C1-0R050J Pd = 1W L1 COILTRONICS CTX62-2-MP DCR = 0.040Ω MPP CORE


VCC

VCC

CAP

SD2

ITH

CT

LTC1149

VIN

SENSE+VFB

SENSE–

D1 1N4148

+

C9 0.01µF

D4 1N4148

+

VIN 10V TO 48V C1

0.1µF

+ C4 1µF

R1 1k

Q3 2N3904

Q4 2N3906

33k

10k 33k

D3 5.1V

432k 1%

49.9k 1%C7

3300pF X7R

C8 200pF NPO

3

5

16

15

7

6

1 4

9

10

8

13

C3 0.047µF Z5U

Q1 IRF9Z34

Q2 IRFZ34

D2 MBR160

C2 330µF 63V

L1 62µH

R2 0.05Ω

VOUT 12V 2A

C10 220µF × 2 10V


2

11

12

14

PGATE

NGATESGND PGND

PDRIVE

RGND

C5 0.1µF

C6 0.068µF

Z5U

10k

Figure 11A. LTC1149: (10V-48V to 12V/2A) High Voltage Buck Converter

LTC1149: (10V-48V to 12V/2A) High VoltageBuck Converter

The LTC1149 contains an internal 10V low dropout linearregulator to provide power to the control circuitry. Itactually means that the DC bias current as well as the gatecharge current come directly from the input line, causingslight efficiency degradation, especially for high inputvoltages (additional power is dissipated by the internalregulator). A solution for this problem is presented inFigure 11A. When the output level reaches about 5V, ZenerD3 starts conducting and saturates Q3, which in turnswitches Q4 on. Now VCC pins 3 and 5 are powered directlyfrom the output. Losses caused by DC current and gatecharge current are significantly reduced allowing im-proved efficiency at high input voltage.

The regulator output must be set up for an output voltageless than 14.5V to provide a margin for the LTC1149 pin5 absolute maximum rating of 16V. It should also be

observed that Q4 turns on when the output is less than 10V(the internal regulator output) and stays on or off under allconditions.

Figure 11B. LTC1149: (10V-48V to 5V/2A) MeasuredEfficiency with Large P-Channel and N-ChannelMOSFETs


EFFI

CIEN

CY (%

)

100

95

90

85

80

75

70

65

600.01 0.1

AN54 • F11B

1 10

VIN = 15V

VIN = 48V

VIN = 36V

Application Note 54

AN54-14

LTC1149: High Power Buck Converters

Figures 12A and 13A are examples of high power (morethan 100W) converters that use the LT1149. The regula-tors are powered from the full wave rectified output of a16VRMS to 32VRMS transformer. Input capacitance is verybulky, but it has to ensure that ripple valleys do not dipbelow the minimum regulator input requirement. Thecircuit in Figure 13A has additional gate driver circuitswhich are required to improve MOSFET switching times.Overall efficiency goes as high as 98%! Remember, atthese output current levels layout becomes extremelyimportant, and all the recommendations from the LTC1149data sheet must be closely followed.

COUT, 1500µF 25V, × 2

PGATE

VIN

VCC

PDRIVE

VCC

CT

ITH

SENSE–

CAP

SD2

RGND

NGATE

PGND

SGND

VFB

SENSE+

SHUTDOWN (NORMALLY GND)

100pF

VIN 16VRMS RECTIFIED

+

+

10µF

0.33µF

0.33µF

R2 205k

100Ω

LTC1149

100Ω

3300pFCT

270pF

470Ω

RS 0.0082Ω

1

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

Q1 RFG60P06E

Q2 IRFZ44

D2 MBR380

D1 1N4148

AN54 • F12A

OUTPUT GROUND CONNECTION

L 33µH

1.5µF 63V WIMA

1µF WIMA

33k

VOUT 13.8V 10A

1000pF

COUT PANASONIC HFQ SERIES D2 MOTOROLA SCHOTTKY Q1 HARRIS PMOS BV DSS = 60V RDSON = 0.03Ω

0.22µF CIN

20000µF 35V

+

R1 20.5k 1%

Figure 12A. LTC1149: (16VRMS to 13.8V/10A) Buck Converter


EFFI

CIEN

CY (%

)

100

95

90

85

80

75

70

650.1 1 10

AN54 • F12B

Figure 12B. LTC1149: (16VRMS to 13.8V/10A)Buck Converter Measured Efficiency

AN54-15

Application Note 54

COUT, 1000µF 35V

PGATE

VIN

VCC

PDRIVE

VCC

CT

ITH

SENSE–

CAP

SD2

RGND

NGATE

PGND

SGND

VFB

SENSE+

SHUTDOWN (NORMALLY GND)

100pF

VIN 32VRMS RECTIFIED

+

+

10µF

0.33µF

MPSW06

MPSA56

PDRIVE BUFFER

NDRIVE BUFFER

0.33µF

R2 432k

100Ω

LTC1149

100Ω

3300pFCT

150pF

470Ω

RS 0.016Ω

1

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

Q1 SMP40P06

Q2 IRFZ34

D2 MBR380

AN54 • F13A

OUTPUT GROUND CONNECTION

L 62µH

1N4148

D1 1N4148

1.5µF 63V WIMA

1µF WIMA

33k

VOUT 27.6V 5A

1000pF

0.22µF

CIN 5000µF 75V

+

R1 20.5k 1%

MPSA56

COUT PANASONIC HFQ SERIES D2 MOTOROLA SCHOTTKY Q1 SILICONIX PMOS BV DSS = 60V RDSON = 0.045Ω

Figure 13A. LTC1149: (32VRMS to 27.6V/5A) Buck Converter


EFFI

CIEN

CY (%

)

100

95

90

85

80

75

70

650.1 1 10

AN54 • F13B

Figure 13B. LTC1149: (32VRMS to 27.6V/5A) Buck Converter Measured Efficiency

Application Note 54

AN54-16

LTC1147: (5V-14V to 5V/1A) Buck Converter withSurface Mount Technology

The LTC1147 (Figure 14A) is a great way to implement ahigh efficiency regulator using a minimum number ofexternal components and occupying the least board space.This regulator provides many advantages of the LTC1148including constant off-time configuration, low dropoutregulation and Bust Mode operation, comes in a smallerpackage and does not require the N-channel MOSFET. Theonly sacrifice made is synchronous rectification whichdegrades the efficiency of this circuit up to three percent-age points. Compare efficiency graphs in Figures 1B and14B! Since the clamp diode D1 conducts all the timeduring the off-time, a larger diode (MBRD330) is used forthis circuit. The LTC1147 is an excellent choice where theoutput current is less than 1A, and where the input voltageis less than twice the output voltage.

Figure 14B. LTC1147: (5V-14V to 5V/1A)Buck Converter Measured Efficiency


50

EFFI

CIEN

CY (%

)

70

80

90

100

0.01 0.1 1

AN54 • F14B

60

VIN = 6V

VIN = 10V

VIN = 14V

AN54 • F14A

C2 AVX (Ta) TPSD226K025R0200 ESR = 0.200Ω IRMS = 0.775A C5 AVX (Ta) TPSE227K010R0080 ESR = 0.080Ω IRMS = 1.285A Q1 SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC D1 MOTOROLA SCHOTTKY VBR = 30V R2 KRL SP-1/2-A1-0R100J Pd = 0.75W L1 COILTRONICS CTX100-4 DCR = 0.175Ω Kool Mµ CORE


ITH

CT

GND

LTC1147-5

VIN

SENSE +

SENSE –

+

C5 0.001µF

+

VIN 5V TO 14V

R1 1k

C3 3300pF X7R

C4 390pF NPO

2

8

5

4

Q1 Si9430DY

D1 MBRD330

C2 22µF x 2 25V

100µH

R2 0.1Ω

5V 1A

C6 220µF 10V

QUIESCENT CURRENT = 190µA TRANSITION CURRENT (Burst Mode OPERATION/ CONTINUOUS OPERATION) = 170mA

1

7

SHUTDOWN6

+

L1

1

2

4

3

C1 0.1µF

3

PDRIVE

Figure 14A. LTC1147: (5V-14V to 5V/1A) Buck Converter with Surface Mount Technology

AN54-17

Application Note 54


50

EFFI

CIEN

CY (%

)

70

80

90

100

0.01 0.1 1

AN54 • F15B

60

VIN = 5V

VIN = 10V

VIN = 14V

Figure 15B. LTC1147: (4V-14V to 3.3V/1A)Buck Converter Measured Efficiency

LTC1147: (4V-14V to 3.3V/1A) Buck Converter withSurface Mount Technology

Figure 15A shows another compact circuit with theLTC1147 series. It generates 3.3V/1A output using thesame configuration as in the previous example. Despitethe lack of synchronous rectification, efficiency approaches95% with 5V input.

AN54 • F15A

C2 AVX (Ta) TPSD226K025R0200 ESR = 0.200Ω IRMS = 0.775A C6 AVX (Ta) TPSE227K010R0080 ESR = 0.080Ω IRMS = 1.285A Q1 SILICONIX BVDSS = 20V DCRON = 0.100Ω CRSS = 400pF Qg = 50nC D1 MOTOROLA R2 KRL SP-1/2-A1-0R100 Pd = 0.75W L1 COILTRONICS CTX100-4 DCR = 0.175Ω Kool Mµ CORE

ITH

CT

GND

LTC1147-3.3

VINPDRIVE

SENSE +

SENSE –

+

C5 0.001µF

+

VIN 4V TO 14V

R1 1k

C3 3300pF X7R

C4 560pF NPO

2

8

5

4

Q1 Si9430DY

D1 MBRD330

C2 22µF × 2 25V

100µH

R2 0.1Ω

3.3V 1A

C6 220µF 10V


1

7

SHUTDOWN6

+

L1

1

2

4

3

C1 0.1µF

3


Application Note 54

AN54-18

LTC1147: (4V-8V to 3.3V/1.5A) Buck Converter withSurface Mount Technology

One more application circuit with LTC1147 is presented inFigure 16A. It is optimized for 5V to 3.3V conversion withinput voltages of 4V to 8V (limited by the P-channelMOSFET). A circuit board has been laid out for this circuitand has subsequently been thoroughly tested under fulloperating conditions and optimized for mass productionrequirements. A Gerber file for the board is available uponrequest.

AN54 • F16A

C1 AVX TPSD476M016R0150 TANTALUM 47µF 16V C6 AVX TPSD107M010R0100 TANTALUM 100µF 10V D1 MOTOROLA MBRS130LT3 BVR = 30V L1 SUMIDA CDR74B-100LC 10 µH Q1 SILICONIX PMOS Si9433 R2 IRC LRC-LR2010-01-R068-F

ALL OTHER CAPACITORS CERAMIC

ITH

CT

GND

LTC1147-3.3

VINPDRIVE

SENSE +

SENSE –

+

C5 0.01µF

+

VIN 4V TO 8V

0V = NORMAL ≥ 2V = SHUTDOWN

R1 1k

C3 3300pF

C4 120pF

2

8

5

4

D1 MBRS130LT3

C1 47µF 16V

R2 0.068Ω

VOUT 3.3V 1.5A

C6 100µF 10V

1

7

SHUTDOWN6

L1 10µH

C2 0.1µF

3

Q1 P-CH

Si9433DY

Figure 16A. LTC1147: (4V-8V to 3.3V/1.5A) Buck Converter with Surface Mount Technology


EFFI

CIEN

CY (%

)

100

95

90

85

80

75

70

65

600.01 0.1 1

AN54 • F16B

LTC1147-3.3 SUMIDA CDR74B

VIN = 5V

LTC1147-3.3 SUMIDA CD54

VIN = 5V

2

Figure 16B. LTC1147: (4V-8V to 3.3/1.5A)Buck Converter Measured Efficiency

AN54-19

Application Note 54

LTC1148: (10V-14V to 5V/10A) High CurrentBuck Converter

Due to differences in physical structure between N- and P-channel MOSFETs, the former are usually more costeffective, more available, and provide better internal pa-rameters for the same size. This is especially importantwhen high output currents are required. With 5A to 10Aoutput currents the use of N-channel MOSFETs in place ofP-channel is the most preferable solution. An implemen-tation of this idea is presented in Figure 17A.

A special Q4 gate drive circuit that uses a bootstrappingtechnique is added to provide required gate drive. Whenpin 1 goes high it turns Q3 on, providing a path for fast Q4gate capacitance discharge. With Q3 off, Q1 and Q2saturate each other feeding positive voltage to Q4’s gate.As a result Q4 turns on, and the positive pulse at its sourceis AC coupled through C6 supplying bootstrapped VCC forthe gate drive “SCR.” The external driver circuit contains

only inexpensive, readily available small-signal transis-tors, yet allows the use of all N-channel MOSFETs. Effi-ciency reaches 96% (see Figure 17B).


50

EFFI

CIEN

CY (%

)

70

80

90

100

1 10

AN54 • F17B

60

VIN = 10V

VIN = 14V

Figure 17A. LTC1148: (10V-14V to 5V/10A) High Current Buck Converter

Figure 17B. LTC1148: (10V-14V to 5V/10A) High CurrentBuck Converter Measured Efficiency

Q4 IRFZ44

AN54 • F17A

C1 (Ta) C7 UNITED CHEMI-CON (Al) LXF35VB272M16 X 40 ESR = 0.018Ω IRMS = 2.900A C8 NICHICON (Al) UPL1C222MRH ESR = 0.028Ω IRMS = 2.010A Q4, Q5 IR NMOS BVDSS = 60V DCRON = 0.028Ω CRSS = 310pF Qg = 69nC D1, D2 MOTOROLA SILICON VBR = 75V D3 MOTOROLA SCHOTTKY VBR = 30V

ITH

CT

SGND PGND

LTC1148-5

VINPDRIVE

SENSE +

SENSE –

NDRIVE

C5 0.001µF

+

VIN 10V TO 14V

C1 1µF

R4 1k

C3 3300pF X7R

C4 820pF NPO

10

4

1

8

7

14

Q5 IRFZ44

D3 1N5818

C6 0.47µF

R8 0.01Ω

5V 10A

C8 2200µF × 3 16V

3

11

12

SHUTDOWN

6

C2 0.1µF

+

Q3 VN2222LL

D1 1N4148

R1 20k

Q1 2N3906

Q2 2N2222

+ C7 2700µF × 2 35V

R6 100

D2 1N4148

R3 220

L1

33µH

R7 22k

R2 220

R5 100

R8 KRL NP-2A-C1-0R010J Pd = 3W L1 COILTRONICS CTX33-10-KM DCR = 0.010Ω Kool Mµ CORE


QUIESCENT CURRENT = 22mA

Application Note 54

AN54-20

Two resistors are placed in series with the current sensepins. This significantly improves circuit noise immunitywhich is of great importance when switching high current.R7, connected between pin 7 and ground, disables BurstMode operation so that the regulator operates continuously.

LTC1149: (12V-36V to 5V/5A) High Current, HighVoltage Buck Converter

Figure 18A shows a high current, high voltage buckconverter. The LTC1149 is used to accommodate the inputvoltage requirement. As in Figure 17A the top N-channelMOSFET is driven by an external circuit which inverts thechip’s P-drive output and uses bootstrapping to providepositive gate-source voltage. The peak-to-peak gate volt-age is defined by the DC portion of the gate driver VCC.Therefore, not to exceed maximum gate voltage for theMOSFET, D1’s anode is connected to internal 10V regula-tor output. In this application PDRIVE pin 4 is used because

an output referenced to ground is required. PGATE pin 1provides the same drive signal referenced to VCC.

Figure 18B. LTC1149: (12V-36V to 5V/5A) High Current, HighVoltage Buck Converter Measured Efficiency


50

EFFI

CIEN

CY (%

)

70

80

90

100

1 5

AN54 • F18B

60

VIN = 12V

VIN = 24V

VIN = 36V

Figure 18A. LTC1149: (12V-36V to 5V/5A) High Current, High Voltage Buck Converter

Q4 MTP30N06EL

AN54 • F18A

C6 0.001µF

+

C7 0.22µF

R7 0.02Ω

5V 5A

C9 220µF × 2 10V

Q3 VN2222LL

D1 1N4148

R2 10k

Q1 2N3906

Q2 2N2222

C8 1000µF 63V

D2 1N4148

R4 220Ω

L1

50µH

R3 220Ω

VCC

VCC

CAP

SD1

SD2

ITH

CT

LTC1149-5

PGATE

VIN

SENSE +

SENSE –

NGATE

VIN 12V TO 36V

C1 0.1µF

+ C2 1µF

C3 0.1µF

R1 1k

C4 3300pF

X7R

C5 820pF NPO

3

5

16

10

15

7

6

4

9

8

13

2

11

12

14

SGND PGND

PDRIVE

RGND

Q5 IRFZ34

D3 MBR160

C2 (Ta) C8 NICHICON (Al) UPL1J102MRH ESR = 0.027Ω IRMS = 2.370A C9 SANYO (OS-CON) 10SA220M ESR = 0.035Ω IRMS = 2.360A Q1 PNP BV CEO = 30V Q2 NPN BVCEO = 40V Q3 SILICONIX NMOS BVDSS = 60V RDSON = 5.000Ω Q4 MOTOROLA NMOS BVDSS = 60V RDSON = 0.050Ω CRSS = 100pF Qg = 40nC

R6 100Ω

R5 100Ω

+

1

Q5 IR NMOS BVDSS = 60V RDSON = 0.050Ω CRSS = 100pF Qg = 32nC D1, D2 SILICON VBR = 75V D3 MOTOROLA SCHOTTKY VBR = 60V R7 KRL NP-2A-C1-0R020J Pd = 3W L1 COILTRONICS CTX50-5-52 DCR = 0.021Ω #52 IRON POWDER CORE


AN54-21

Application Note 54


The circuit in Figure 19A uses the same configuration butis designed to provide up to 10A output current. Besidesthe usual external component changes, the circuit useshigher current MOSFETs to improve efficiency at maxi-mum power levels. Efficiency at 5A output is severalpercentage points better than in the previous example(compare Figures 18B and 19B). R7 keeps the regulator incontinuous mode causing the rapid efficiency decrease atlighter loads.

Figure 19B. LTC1149: (12V-48V to 5V/10A) High Current,High Voltage Buck Converter Measured Efficiency


50

EFFI

CIEN

CY (%

)

70

80

90

100

1 10

AN54 • F19B

60

VIN = 12V

VIN = 48V

VIN = 36V

VIN = 24V

Q4 IRFZ34

AN54 • F19A

C6 0.001µF

+

C7 0.22µF

R8 0.01Ω

5V 10A

Q3 VN2222LL

D1 1N4148

R2 20k

Q1 2N3906

Q2 2N2222

C8 1000µF × 2 63V

D2 1N4148

R4 220Ω

L1

33µH

R3 220Ω

VCC

VCC

CAP

SD1

SD2

ITH

CT

LTC1149-5

PGATE

VIN

SENSE +

SENSE –

NGATE

VIN 12V TO 48V

C1 0.1µF

+ C2 1µF

C3 0.1µF

R1 1k

C4 3300pF

X7R

C5 820pF NPO

3

5

16

10

15

7

6

1

4

9

8

13

2

11

12

14

SGND PGND

PDRIVE

RGND

Q5 IRFZ44

D3 MBR160

C2 (Ta) C8 NICHICON (Al) UPL1J102MRH ESR = 0.027Ω IRMS = 2.370A C9 NICHICON (Al) UPL1C222MRH ESR = 0.028Ω IRMS = 2.010A Q1 PNP BVCEO = 30V Q2 NPN BVCEO = 40V Q3 SILICONIX NMOS BVDSS = 60V RDSON = 5.000Ω Q4 IR NMOS BVDSS = 60V RDSON = 0.050Ω CRSS = 100pF Qg = 32nC Q5 IR NMOS BVDSS = 60V RDSON = 0.028Ω CRSS = 310pF Qg = 69nC

R6 100Ω

R5 100Ω

+

R7 22k

QUIESCENT CURRENT = 26mA

+

C9 220µF × 3 16V

D1, D2 SILICON VBR = 75V D3 MOTOROLA SCHOTTKY VBR = 60V R8 KRL NP-2A-C1-0R010J Pd = 3W L1 COILTRONICS CTX33-10-KM DCR = 0.010Ω Kool Mµ CORE



Application Note 54

AN54-22


9

8

Q4 IRFZ44

AN54 • F20A

C7 0.001µF

C7 0.22µF

24V 10A

C10 1000µF × 3 35V

Q3 VN2222LL

D1 IN4148

R3 20k

Q1 2N5087

Q2 MPS651

C8 1000µF × 2 63V

D2 1N4148

R2 5.1k

L1

50µH

VCC

VCC

CAP

SD2

ITH

CT

LTC1149

PGATE

VIN

VFB

SENSE +

NGATE

VIN 32V TO 48V

C1 0.1µF

+ C2 1µF

C3 0.1µF

R1 1k

C4 3300pF

X7R

C5 270pF NPO

3

5

16

15

7

6

4

10

13

2

11

12

14

SGND PGND

PDRIVE

RGND

Q5 IRFZ44

C2 (Ta) C9 NICHICON (Al) UPL1J102MRH ESR = 0.027Ω IRMS = 2.370A C10 NICHICON (Al) UPL1V102MRH ESR = 0.029Ω IRMS = 1.980A Q4, Q5 IR NMOS BVDSS = 60V RDSON = 0.028Ω CRSS = 310pF Qg = 69nC Q1 PNP BVCEO = 50V Q2 NPN BVCEO = 60V D1, D2, D3, D4 SILICON VBR = 75V D5 MOTOROLA SCHOTTKY VBR = 60V R10 KRL NP-2A-C1-0R010J Pd = 3W L1 COILTRONICS CTX50-10-KM DCR = 0.010Ω Kool Mµ CORE


100Ω

R6 100Ω

+

SENSE –

1

C6 100pF

R8 220k 1%

R5 220Ω

D3 1N4148

R4 220Ω

D4 1N4148

R9 12k 1%

D5 MBR160

R10 0.01Ω

R7

VOUT = 1.25V (1 + R8/R9) QUIESCENT CURRENT = 26mA TRANSITION CURRENT (Burst Mode OPERATION/CONTINUOUS OPERATION) = 1.5A

+

+

R11 39k


If an output voltage other than 5V or 3.3V is required, anadjustable version of the regulator must be used. A 24V/10A example is shown in Figure 20A. The output voltageis set by resistors R8 and R9. The LTC1149 monitors VFB(pin 10) keeping it at 1.25V. Similar to the previous twocircuits, an external gate driver is added to switch theN-channel MOSFET Q2. To ensure consistent start-up ofthe bootstrapping circuitry, the driver is initially poweredby R2 and D2. (The main requirement at start-up is tosupply the driver with VCC that exceeds output targetvoltage.) After the switching starts, D1 an D3 power theexternal gate drive circuit.

OUTPUT CURRENT (mA)10

50

EFFI

CIEN

CY (%

)

70

80

90

100

100 1A 10A

AN54 • F20B

60

VIN = 32V

VIN = 45V

Figure 20B. LTC1149: (32V-48V to 24V/10A) High Current,High Voltage Buck Converter Measured Efficiency

AN54-23

Application Note 54

LT1148: (4V-14V to 5V/1A) SEPIC Converter

Figure 21A provides the function of a step-up and step-down converter without using a transformer. This topol-ogy is called a SEPIC converter. The P-channel transistorand L1 are arranged similarly to a buck-boost topologyproviding the boost part of the regulator. Pulses at Q2’sdrain (actually two paralleled devices) are coupled via C8to the buck portion that includes Q3 and L2. This circuitaccepts 4V to 14V input and provides a solid 5V output.Even though the schematic shows two inductors, theycarry the same current and can be wound on a single core.Such dual coils are readily available (see circuit parts list).This topology is acceptable for moderate loads only, as thecoupling capacitor C8 carries the full load current andmust be sized accordingly. When the sense resistor isplaced at ground potential, such as the case in this circuit,the off-time increases approximately 40%.

An adjustable version of the regulator is required when the


50

EFFI

CIEN

CY (%

)

70

80

90

100

0.01 0.1 1

AN54 • F21B

60

VIN = 14V

VIN = 4V

VIN = 5V

VIN = 4V

VIN = 10V

VIN = 5V

current sense resistor is placed at ground. This allows toprovide different output voltages. D2 is included for foldbackshort-circuit protection. When VOUT equals zero (output isshorted) D2 clamps pin 6 and limits the output current.

Figure 21B. LTC1148: (4V-14V to 5V/1A)Buck-Boost Converter Measured Efficiency

Figure 21A. LTC1148: (4V-14V to 5V/1A) SEPIC Converter

AN54 • F21A

C6 0.1µF

VOUT 5V 1A

C10 220µF 10V

Q2 Si9430DY x 2

C7 100µF 20V

VIN 4V TO 14V C1

1µF

C2 0.1µF

R1 1k

C4 3300pF

X7R

C5 390pF NPO

5

10

6

4

1

9

8

7

D2 MBR0520L

14

3

11

12

D1 1N5818

C1 (Ta) C7 SANYO (OS-CON) 20SA100M ESR = 0.037Ω IRMS = 2.250A C8, C10 SANYO (OS-CON) 10SA220M ESR = 0.035Ω IRMS = 2.360A Q2 SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC Q3 SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC D1 MOTOROLA SCHOTTKY VBR = 30V R2 KRL NP-1A-C1-0R082J Pd = 1W L1 COILTRONICS CTX50-4P, CTX50-5P


+

R2 0.082Ω

TO VOUT

SHUTDOWN

ITH

CT

LTC1148

PDRIVE

VIN

SENSE +

NDRIVESGND PGND

VFB

SENSE –

INT VCC

C8 220µF 10V

L1 50µH

Q3 Si9410DY

R3 75k 1%

R4 25k 1%

+

C9 100pF

+ +

L2 50µH

VOUT = 1.25V (1 + R3/R4) QUIESCENT CURRENT = 200µA TRANSITION CURRENT (Burst Mode OPERATION/ CONTINUOUS OPERATION) = 250mA/VIN = 5V

Application Note 54

AN54-24


50

EFFI

CIEN

CY (%

)

70

80

90

100

0.01 0.1 0.5

AN54 • F22B

60

VIN = 14V VIN = 4V

VIN = 10V VIN = 5VLTC1148: (4V-14V to 5V/0.5A, – 5V/0.5A)Split Supply Converter

Applications requiring a split supply can use the circuitpresented in Figure 22A. It contains the converter fromFigure 21A and adds a synchronous charge pump Q4 toprovide a –5V output. Q4 source is referenced to the –5Vline, and its gate drive is AC coupled via C11 and clampedby D3. The outputs exhibit excellent tracking with line andload changes. This is a great way to build a dual outputconverter without any transformer.

SENSE –

AN54 • F22A

C7 0.1µF C10

220µF 10V

Q2 Si9430DY

C8 100µF 20V

VIN 4V TO 14V C1

1µF

C2 0.1µF

R1 1k

C4 3300pF

X7R

C5 390pF NPO

5

10

6

4

1

8

7

9

14

3

11

12

D1 1N5818

C1 (Ta) C8 SANYO (OS-CON) 20SA100M ESR = 0.037Ω IRMS = 2.250A C9, C10, C12 SANYO (OS-CON) 10SA220M ESR = 0.035Ω IRMS = 2.360A Q2 SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC Q3, Q4 SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC D1, D2 MOTOROLA SCHOTTKY VBR = 30V R2 KRL NP-1A-C1-0R082J Pd = 1W L1 COILTRONICS CTX50-4

+

R2 0.05Ω

VOUT

SHUTDOWN

ITH

CT

LTC1148

PDRIVE

VIN

SENSE +

NDRIVESGND PGND

VFB

INT VCC

C9 220µF 10V

L1 50µH

Q3 Si9410DY

R3 75k 1%

R4 25k 1%

C11 0.22µF

+ +

L2 50µH

VOUT = 1.25V (1 + R3/R4) QUIESCENT CURRENT = 250µA TRANSITION CURRENT (DIS/CONT) = 130mA/VIN = 5V

C6 100pF

R5 51k

D3 1N4148

C12 220µF 10V

–VOUT –5V 0.5A

+VOUT 5V 0.5A

+

+

Q4 Si9410DY

D2 1N5818

D4 MBR0520L

Figure 22A. LTC1148: (4V-14V to 5V/0.5A, – 5V/0.5A) Split Supply Converter

Figure 22B. LTC1148: (4V-14V to 5V/0.5A, –5V/0.5A)Split Supply Converter Measured Efficiency

AN54-25

Application Note 54

LTC1148: (4V-10V to –5V/1A) Positive-to-NegativeConverter

Figure 23A shows a buck-boost converter using theLTC1148. This is an inverting topology, and it can inher-ently buck or boost the input voltage. Ground pins of thechip are referenced to the output line; no additional levelshifting circuit is required to drive the N-channel FET Q3(its source is referenced to – 5V as well). Now even withminimum input level, the circuit provides a solid 9V peak-to-peak MOSFET drive signal. However, so as not toexceed absolute maximum voltage at pin 3, the input lineis limited to 10V. If the circuit is required to accept a higherinput voltage, the LTC1148HV can be used instead. Q1 isadded to provide a logic level shutdown feature. If shut-down is not needed omit Q1 and R1, and short pin 10 topin 11.

Figure 23A. LTC1148: (4V-10V to –5V/1A) Positive-to-Negative Converter


EFFI

CIEN

CY (%

)

100

95

90

85

80

75

70

65

600.01 0.1

AN54 • F23B

1 10

4V TO –5V/1A

10V TO –5V/1A

Figure 23B. LTC1148: (4V-10V to – 5V/1A)Positive-to-Negative Converter MeasuredEfficiency

SENSE –

AN54 • F23A

C5 0.01µF

C8 220µF × 2 10V

Q2 Si9430DY

C7 150µF × 2 16V

VIN 4V TO 10V

C1 1µF

C2 0.1µF

R2 1k

C3 6800pF

X7R

C4 560pF NPO

5

10

6

4

1

8

7

9 14

3

11

12

D1 1N5818

C1 (Ta) C7 SANYO (OS-CON) 16SA150M ESR = 0.035Ω IRMS = 2.280A C8 SANYO (OS-CON) 10SA220M ESR = 0.035Ω IRMS = 2.360A Q2 SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC Q3 SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC D1 MOTOROLA SCHOTTKY VBR = 30V R2 KRL NP-1A-C1-0R050J L1 COILTRONICS CTX50-2-MP DCR = 0.032Ω MPP CORE


+

R2 0.05Ω

Q1 TP0610L

SHUTDOWN

ITH

CT

LTC1148

PDRIVE

VIN

SENSE +

NDRIVESGND PGND

VFB

INT VCC

L1 50µH

Q3 Si9410DY

R3 75k 1%

R4 25k 1%

+

VOUT = 1.25V (1 + R3/R4)

C6 200pF

– 5V 1A

+ R1 1M

SHUTDOWN

Application Note 54

AN54-26

LTC1148: (5V-12V to –15V/0.5A) Buck-BoostConverter

Figure 24A presents an inverting regulator designed toaccommodate higher output voltages. The LTC1148 can-not accept feedback directly from a negative output. Toregulate negative outputs, the feedback must be invertedand compared against 1.25V. This function is provided bya DC level shifting amplifier consisting of Q1 and associ-ated components. Resistor R4 provides amplifier negativefeedback, effectively cancelling variations in VCC, and Q2provides temperature compensation. The output voltageis set by resistors R4 and R5. As usual, with the senseresistor at ground potential, the off-time increases roughlyby 40%.


EFFI

CIEN

CY (%

)

95

90

85

80

75

70

650.01 0.1 1

AN54 • F24B

5V TO –15V/0.5A

12V TO –15V/0.5A

Figure 24B. LTC1148: (5V-12V to –15V/0.5A)Buck-Boost Converter Measured Efficiency

AN54 • F24A

C8 0.01µF

C9 47µF 25V

Q3 Si9435DY × 2

C7 220µF 10V

C6 200pF

C5 6800pF

10

6

4

11

1

8

7

9

12

3

U1

D3 MBR735

R7 DALE LVR-3 0.033W L1 COILTRONICS CTX50-5-52 C7 SANYO OS-CON 105A220K C9, C10 SANYO OS-CON 255C47K

+

R7 0.033Ω

Q2 2N5210

Q1 2N5210

LTC1148

VIN

SHUTDOWN

ITH

CT

SGND

PDRIVE

SENSE+

SENSE–

VFB

PGND

L1 50µH

R4 49.9k 1%

+

+ C10 47µF 25V

C2 0.1µF

C3 1µF

C11 200pF

R6 1k

R3 56k

> 1.5V = SHUTDOWN

R5 634k 1%

VOUT –15V 0.5A

VIN 5V TO 12V

+

Figure 24A. LTC1148: (5V-12V to –15V/0.5A) Buck-Boost Converter

AN54-27

Application Note 54

LTC1148: (2V-5V to 5V/1A) Boost Converter

Even though the LTC1148 is mainly used in step-downconverters, it can also show excellent performance in theboost configuration. A boost implementation is shown inFigure 25A. This is a two-cell to 5V converter that uses theLT1109 to provide 12V to power the main regulator chip(unfortunately, MOSFETs do not operate with only 2V at thegate). The LT1109 is a small micropower IC that requiresonly three external components and provides great effi-ciency. An N-channel transistor is used as the switch, andgeneral purpose MOSFETs Q1 and Q2 are used to form aninverting gate driver. When Q3 turns off, the voltage at itsdrain rises above VIN, and a Schottky diode D2 startsconducting. In a short period of time Q4 shorts it outproviding a synchronous rectification feature and increas-ing efficiency. If 12V is already available, the LT1109 can beomitted and the 12V line connected directly to pin 3.

Figure 25A. LTC1148: (2V-5V to 5V/1A) Boost Converter

Q1 TP0610L

SENSE –

AN54 • F25A

C6 0.001µF

C8 220µF × 2 10V

VIN 2V TO 5V

C1 100µF 10V

R2 1k

C4 6800pF

X7R

C5 390pF NPO

10

6

4

1

12V

8

7

9

14

3

11

12

D2 1N5818

C1 SANYO (OS-CON) 10SA100M ESR = 0.045Ω IRMS = 1.870A C3 (Ta) C8 SANYO (OS-CON) 10SA220M ESR = 0.035Ω IRMS = 2.360A Q3, Q4 SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC D1, D2 MOTOROLA SCHOTTKY VBR = 30V

SHUTDOWN

ITH

CT

LT1109

PDRIVE

VIN

SENSE +

NDRIVESGND PGND

VFB

L1 33µH

Q2 VN2222LL

R3 75k 1%

+

C7 100pF

5V 1A

R1 0.05Ω

VIN

SENSE

GND

S/D7

3

1

4

8

D1 1N5818

SHUTDOWN

C2 0.1µF

C3 1µF

+

Q3 Si9410

L2 25µH

R4 25k 1%

Q4 Si9410

+

SW

LTC1148

VR1

R2 KRL SL-1-C1-0R050J Pd = 1W L1 COILTRONICS CTX33-1 DCR = 0.220Ω Kool Mµ CORE L2 COILTRONICS CTX25-4

VOUT = 1.25V (1 + R3/R4)

Figure 25B. LTC1148: (2V-5V to 5V/1A)Boost Converter Measured Efficiency


EFFI

CIEN

CY (%

)

100

95

90

85

80

75

70

650.01 0.1 1

AN54 • F25B

4V TO 5V/1A

2V TO 5V/1A

Application Note 54

AN54-28

LTC1143: (5.2V-14V to 3.3V/2A and 5V/2A)Dual Buck Converter

A circuit that provides dual 3.3V/5V output is shown inFigure 26A. It uses a dual LTC1143 regulator that com-bines two LTC1147, non-synchronous switching regula-tors. The efficiency was measured with only one outputloaded which provided worse results for low output cur-rent due to the presence of the second half’s quiescentcurrent. This circuit provides very simple means to powerdual voltage logic. It occupies small amount of boardspace and is very efficient! OUTPUT CURRENT (A)

0.001

EFFI

CIEN

CY (%

)

95

90

85

80

75

70

65

600.01 0.1

AN54 • F26B

1 10

14V TO 3.3V

8V TO 5V

8V TO 3.3V

14V TO 5V

Figure 26B. LTC1143: (5.2V-14V to 3.3V/2A and 5V/2A)Dual Buck Converter Measured Efficiency

+

+ +

PDRIVE3

SENSE+ 3

SENSE– 3

GND3 GND5CT3 ITH3 ITH5 CT5

SENSE– 5

SENSE+ 5

PDRIVE5

VIN3 SHUTDOWN 5 VIN5

LTC1143

CT5 200pF

CT3 390pF

3 14 15 7 6 11

RC5 1k

CC3 3300pF

CC5 3300pF

RC3 1k

13 10 5

12

9

8

4

1

16

VOUT5 5V/2A

COUT5 220µF 10V × 2

RSENSE5 0.05Ω

L2 20µH

D2 MBRD330

RSENSE: KRL SL-1R050J L1, L2: COILTRONICS CTX20-4 CIN3, CIN5: AVX (Ta) TPSD226K025R0200 COUT3, COUT5: AVX (Ta) TPSE227K010R0080 Q1, Q2: SILICONIX PMOS Si9430DY

D1 MBRD330

0V = NORMAL >1.5V = SHUTDOWN

CIN5 22µF 25V × 2

CIN3 22µF 25V × 2 Q1

P-CH Si9430DY

COUT3 220µF 10V × 2

L1 20µH

RSENSE3 0.05ΩVOUT3

3.3V/2A

VIN 5.2V TO 14V

+

Q2 P-CH

Si9430DY

0.01µF 0.01µF

AN54 • F26A

0.22µF0.22µF

SHUTDOWN 32

Figure 26A. LTC1143: (5.2V-14V to 3.3V/2A and 5V/2A) Dual Buck Converter

AN54-29

Application Note 54

Figure 27B. LTC1148HV-5: (5.2V-18V to 5V/1A) HighVoltage Buck Converter Measured Efficiency

LTC1148HV-5: (5.2V-18V to 5V/1A) High VoltageBuck Converter

The standard LTC1148 input voltage is limited to 16Vabsolute maximum level, which is not sufficient in someapplications. Figure 27A shows a step-down regulatorusing the high voltage LTC1148HV. It contains the sameinternal functions but accepts up to 20V input (remember,MOSFET’s gates are usually rated at 20V maximum). As abuilding block it can be used in the same manner asLTC1148. Input tantalum capacitors now have to be ratedat 35V to ensure reliable operation under maximum inputvoltage.


EFFI

CIEN

CY (%

)

100

95

90

85

80

75

70

65

60

550.01 0.1 1

AN54 • F27B

7V TO 5V

12V TO 5V

18V TO 5V

1

2

3

4

5

6

7

14

13

12

11

10

9

8

PDRIVE

NC

VIN

CT

INT VCC

ITH

SENSE–

NDRIVE

NC

PGND

SGND

SHUTDOWN

NC

SENSE+

LTC1148HV-5

+ 1µF

1000pF R1 0.1Ω

SHUTDOWN

L1 50µH

Q2, Si9410DY

D1 MBRS140T3

Q1 Si9430DY

+ CIN 10µF 35V × 2

VIN 5.2V TO 18V

+COUT 220µF 10V AVX

VOUT 5V/1A

CC 3300pF

RC 1k

CT 220pF

CIN COUT L1 R1 Q1 Q2

AVX (Ta) TPSD106K035R0300 AVX (Ta) TPSE227K010R0080 COILTRONICS CTX50-4 KRL SP-1/2-A1-0R100 SILICONIX PMOS Si9430DY SILICONIX NMOS Si9410DY

AN54 • F27A

Figure 27A. LTC1148HV-5: (5.2V-18V to 5V/1A) High Voltage Buck Converter

Application Note 54

AN54-30


EFFI

CIEN

CY (%

)

100

95

90

85

80

75

70

65

600.01 0.1 1

AN54 • F28B

18V to 3.3V

4V to 3.3V

12V to 3.3V

Figure 28B. LTC1148HV-3.3: (4V-18V TO 3.3V/1A)High Voltage Buck Converter Measured Efficiency

LTC1148HV-3.3 (4V-18V to 3.3V/1A) High VoltageBuck Converter

Figure 28A: Here is a high voltage version of the circuitshown in Figure 4A with input voltage increased to 18V.

1

2

3

4

5

6

7

14

13

12

11

10

9

8

PDRIVE

NC

VIN

CT

INT VCC

ITH

SENSE–

NDRIVE

NC

PGND

SGND

SHUTDOWN

NC

SENSE+

LTC1148HV-3.3

+ 1µF

1000pF 0.1Ω

SHUTDOWN

L1 50µH

Q2, Si9410DY

D1 MBRS140T3

Q1 Si9430DY

+ CIN 22µF 35V × 2

VIN 4V TO 18V

+COUT 220µF 10V

VOUT 3.3V/1A

CC 3300pF

RC 1k

CT 270pF

CIN COUT L1 R1 Q1 Q2

AVX (Ta) TPSE226K035R0300 AVX (Ta) TPSE227K010R0080 COILTRONICS CTX50-4 Kool Mµ CORE IRC LR2010-01-R100-G SILICONIX PMOS Si9430DY SILICONIX NMOS Si9410DY

AN54 • F28A

Figure 28A. LTC1148HV-3.3: (4V-18V to 3.3V/1A)High Voltage Buck Converter

AN54-31

Application Note 54

LTC1148HV: (12.5V-18V to 12V/2A) High VoltageBuck Converter

Figure 29A is another application of the LTC1148HV whichis configured as a step-down converter to provide 12V/2Aoutput. With this low dropout regulator, the input can goas low as 12.5V and still produce a regulated output.Resistors R2 and R3 set the output voltage level.


EFFI

CIEN

CY (%

)

100

95

90

85

80

75

70

65

600.01 0.1

AN54 • F29B

1 10

Figure 29B. LTC1148HV: (16V to 12V/2A) High VoltageBuck Converter Measured Efficiency

C1 (Ta) C7 SANYO (OS-CON) 16SA150M Q1 SILICONIX PMOS BVDSS = 20V RDSON = 0.100Ω CRSS = 400pF Qg = 50nC Q2 SILICONIX NMOS BVDSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 30nC D1 MOTOROLA SCHOTTKY VBR = 40V R2 KRL SL-1-C1-0R050J Pd = 1W L1 COILTRONICS CTX47-5P

ITH

CT

LTC1148HV

VIN

SENSE +

SENSE –

+

C6 0.01µF

100pF

+

VIN 12.5V TO 18V

C1 1µF

R1 1k

C4 3300pF X7R

C5 150pF NPO

10

4

1

8

7

9

14

Q1 Si9430DY

Q2 Si9410DY

D1 MBRS140T3

C3 22µF x 2 35V

47µH

R2 0.05Ω

432k 1%

12V 2A

C7 150µF × 3 16V

3

11

12

SHUTDOWN

6

C2 0.1µF

+

AN54 • F29A

SGND PGND

PDRIVE

VFB

NDRIVE

49.9k 1%

Figure 29A. LTC1148HV: (12.5V-18V to 12V/2A) High Voltage Buck Converter

Application Note 54

AN54-32

Figu

re 3

0A. L

TC11

42: (

6.5V

-14V

to 3

.3V/

2A, 5

V/2A

, 12V

/0.1

5A) T

riple

Out

put B

uck

Conv

erte

r

AN

54 •

F30

A

2SH

UTDO

WN3

25C T

327

I TH3

26IN

T V C

C3

16SH

UTDO

WN5

11C T

513

I TH5

12IN

TVCC

55

NC

4P G

ND3

22NC

23P D

RIVE

37

NC6

N DRI

VE3

1SE

NSE+ 3

28SE

NSE– 3

9P D

RIVE

521

NC20

N DRI

VE5

15SE

NSE+ 5

14SE

NSE– 5

8NC

18P G

ND5

19NC

S GND

3S G

ND5

V IN5

V IN3

173

2410

LTC1

142

C4

3300

pF R8

510Ω

C17

200p

F 50

V

C1

3300

pF

R7

510Ω

C16

390p

F 50

V

C14

1µF

50V

C15

1µF

50V

C19

1000

pF

R5

18k

SHDN

4NC

46

NC6

7NC

7

V OUT

ADJ

215

V IN

GND

LT11

21CS

8C1

0 20

pF

R3

649k

1% R4

29

4k

1%

Q1

VN70

02

1 2

3

38

C9

22µF

25

V

+

Q3

Si94

10DY

D2

MBR

S140

+C6

22

µF

25V

+C7

22

µF

25V

R2

100Ω R1

10

0Ω

R10

0.04

0Ω

+C2

0 22

0µF

10V

+C2

1 22

0µF

10V

109

87

12

34

D3

MBR

S140R6

22

C13

1000

pF

C5

0.1µ

F

30µH

, 2A

LPE-

6562

-A02

6

+C8

22

µF

35V

Q5

Si94

10DY

D1

MBR

S140

+C2

22

µF

25V

+C3

22

µF

25V

32

41

L1

33µH

2A

CT

X33-

4

+C1

1 10

0µF

10V

R9

0.05

0Ω

+C1

2 10

0µF

10V

+ –

+ –

12V

ENAB

LE

–VIN

SHUT

DOW

N (T

TL IN

PUT)

SHUT

DOW

N (T

TL IN

PUT)

+VIN

6.

5V T

O 14

VQ4

Si

9430

DY

Q2

Si94

30DY

4

0V =

12V

OFF

>3

V =

12V

ON

(6V

MAX

) DO

NOT

FLO

AT

C18

2200

pF

T16 51.

8T SHUT

DOW

N PI

NS 2

AND

16

MUS

T AC

TIVE

LY B

E DR

IVEN

EI

THER

HIG

H OR

LOW

AND

NOT

ALL

OWED

TO

FLOA

T.

+ –

3.3V

/2A

12V/

150m

A

C2, C

3, C

6, C

7, C

9 C1

1, C

12

C20,

C21

L1

AVX

(Ta)

TPS

D226

M02

5R02

00

AVX

(Ta)

TPS

D107

K010

R010

0 AV

X (T

a) T

PSE2

27M

010R

0100

CO

ILTR

ONIC

S CT

X33-

4

R9

R10

T1

IRC

LR25

12-R

050

IRC

LR25

12-R

040

DALE

, LPE

-656

2-AO

26

5V/2

A

AN54-33

Application Note 54

LTC1142: (6.5V-14V to 3.3V/2A, 5V/2A, 12V/0.15A)Triple Output Buck Converter

LTC1142 is a dual output synchronous switching regula-tor controller. Two independent controller blocks(LTC1148-based) simultaneously provide 3.3V and 5Voutputs. The circuit in Figure 30A shows an application ofthis IC; it generates triple output voltages with 12V forflash memory programming in addition to the usual logicpower levels. The 3.3V section is a regular buck convertercircuit, the 5V section contains an off-the-shelf trans-former T1 in place of the inductor. The secondary windingis used to boost the output level which is rectified andregulated by an LT1121 to provide a clean and stable 12Voutput. A turns ratio of 1:1.8 is used to ensure that theinput voltage to the LT1121 is high enough to keep theregulator out of dropout. With LTC1142 synchronousswitching, the auxiliary 12V output may be loaded withoutregard to the 5V primary output load as long as the loopremains in continuous operation mode. Continuous op-eration is ensured by R5 which inhibits Burst Modewhenever the 12V output is enabled (enable line goeshigh). Make sure that the enable lines are not floating andare driven by TTL level signals. A circuit board has beenlaid out for this circuit and has subsequently been thor-oughly tested under full operating conditions and opti-mized for mass production requirements. A Gerber file forthe board is available upon request.


60

EFFI

CIEN

CY (%

)

65

100

0.01 2.5

AN54 • F30B

0.1

80

1

90

70

75

85

95

LTC1142-3.3 VIN = 8V

LTC1142-5 VIN = 8V

Figure 30B. LTC1142:(6.5V-14V to 3.3V/2A, 5V/2A,12V/0.15A) Triple Output Buck ConverterMeasured Efficiency

Application Note 54

AN54-34

LTC1142HV: (6.5V-18V to 3.3V/2A, 5V/2A, 12V/0.15A)High Voltage Triple Output Buck Converter

Figure 31A shows the same configuration as Figure 30Ausing the high voltage LTC1142HV. Circuit operation isidentical, but now it can accept up to 18V at the input.


60

EFFI

CIEN

CY (%

)

65

100

0.01 2.5

AN54 • F30B

0.1

80

1

90

70

75

85

95

LTC1142-3.3 VIN = 8V

LTC1142-5 VIN = 8V

Figure 31B. LTC1142HV: (6.5V-18V to 3.3V/2A, 5V/2A,12V/0.15A) Measured Efficiency

Figure 31A. LTC1142HV: (6.5V-18V to 3.3V/2A, 5V/2A, 12V/0.15A) High Voltage Triple Output Buck Converter

+

+ +

1000pF

PDRIVE3

SENSE+3

SENSE –3

NDRIVE3

PGND3 SGND3 CT3 ITH3 ITH5 CT5 SGND5 PGND5

NDRIVE5

SENSE–5

SENSE+5

PDRIVE5

VIN3 SHUTDOWN 3 SHUTDOWN 5 VIN5

LTC1142HV

CT5 200pF

4 3 25 27 13 11 17 18

510Ω

3300pF 3300pFCT3 390pF

510Ω

1µF

224 16 10

9

15

14

20

23

1

28

6

VOUT5 5V/2A

C4 220µF

10V × 2

22µF 35V

RSENSE5 0.04Ω

1.8T 30µH

D2 MBRS140

Q3 Si9410DY

0V = NORMAL >1.5V = SHUTDOWN

1µF

C2 22µF 25V × 2

C1 22µF 25V × 2

VIN 6.5V TO 18V

Q4 Si9430DY

Q5 Si9410DY

D1 MBRS140

C3 100µF 10V × 2

L1 33µH

RSENSE3 0.05ΩVOUT3

3.3V/2A

AN54•F31A

+ +

Q2 Si9430DY

2000pF

C1, C2 C3, C4 L1 RSENSE3 RSENSE5 T1

AVX (Ta) TPS226K035R0300 AVX (Ta) TPSD227K010R0100 COILTRONICS CTX33-4 KRL SL-C1-1/2-0R050J KRL SL-C1-1/2-0R040J DALE LPE-6562-A026 PRIMARY: SECONDARY = 1:1.8

22Ω

R1 100Ω

T1

12V ENABLE 0V = 12V OFF >3V = 12V ON

(6V MAX)

1000pF

D3 MBRS140

R3 660k

R4 300k

20pF+

22µF 25V

12V/150mA

LT1121

VOUT

SHUTDOWN

VIN

ADJ

R2 100Ω

Q1 VN7002

R5 18k

+

GND

+

AN54-35

Application Note 54

LTC1148: High Efficiency Charger Circuit

The LTC1148 regulator can be used as a highly efficientbattery charging device. Figure 32 shows a circuit that isprogrammable for 1.3A fast charge or 100mA tricklecharge mode. During the fast charge interval, the resistordivider network (R4 and R5) forces the LTC1148 feedbackpin below 1.25V causing the regulator to operate at themaximum output current. Sense resistor R3 controls thecurrent at approximately 1.3A. When the batteries aredisconnected, the error amplifier sets the output voltage tobe 8.1V (for proper operation this voltage should exceed

maximum possible voltage across the battery pack). Di-ode D2 prevents the batteries from discharging throughthe divider network when the charger is shut down.

Dual rate charging is controlled by Q3 which selectsbetween fast and trickle charge. When the transistor turnson, R1 limits error amplifier output so that the currentlimiter starts operating at 100mA. If the trickle chargecurrent needs to be altered, adjust R1. With 1.3A outputcurrent, this charger is capable of efficiency in excess of90% which minimizes power dissipated in surface mountcomponents.

C1 (Ta) C3 AVX (Ta) TPSD226K025R0100 ESR = 0.100 I RMS = 0.775A C8 AVX (Ta) TPSE227M010R0100 ESR = 0.100I RMS = 1.149A Q1 SILICONIX PMOS BV DSS = 20V RDSON = 0.125Ω CRSS = 400pF Qg = 25nC θJA = 50°C/W Q2 SILICONIX NMOS BV DSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 50nC θJA = 50°C/W D1, D2 MOTOROLA SCHOTTKY VBR = 40V R3 KRL SP-1/2-A1-0R100J Pd = 0.75V L1 COILTRONICS CTX50-4 DCR = 0.175 IDC = 1.350A Kool M µ CORE


VOUT = 1.25V • (1 + R4/R5) = 8.1V FAST CHARGE = 130mV/R3 = 1.3A TRICKLE CHARGE = 100mA EFFICIENCY > 90%

ITH

CT

LTC1148

VIN

SENSE +

SENSE –

+

C6 0.01µF

C7 100pF

+

VIN 8V TO 15V

C1 1µF

R2 1k

R1 51Ω

C4 3300pF X7R

C5 200pF NPO

10

0V = NORMAL > 1.5A = SHUTDOWN

4

1

8

7

9

14

Q1 Si9430DY

Q2 Si9410DY

D1 MBRS140T3

D2 MBRS340T3

C3 22µF × 2 35V

R3 0.1Ω

R4 274k 1%

VOUT

C8 220µF 10V

3

11

12

Q3 VN2222LL

“1” TRICKLE CHARGE

SHUTDOWN

6

C2 0.1µF

+

L1 50µH1

2

4

3

AN54 • F32

SGND PGND

PDRIVE

VFB

NDRIVE

VBAT 4 CELLS

R5 49.9k 1%

Figure 32. LTC1148: High Efficiency Charger Circuit

Application Note 54

AN54-36

LTC1148: High Voltage Charger Circuit

Figure 33 is a variation of Figure 32. It is designed tocharge 6 cells and uses the LTC1148HV for higher inputvoltages. R4 value has been changed to provide 12.3Voutput when the battery is not connected.

C1 (Ta) C3 AVX (Ta) TPSD226K035R0200 ESR = 0.200 I RMS = 0.663A C8 AVX (Ta) TPSE107M016R0100 ESR = 0.100I RMS = 1.149A Q1 SILICONIX PMOS BV DSS = 20V RDSON = 0.125Ω CRSS = 400pF Qg = 25nC θJA = 50°C/W Q2 SILICONIX NMOS BV DSS = 30V RDSON = 0.050Ω CRSS = 160pF Qg = 50nC θJA = 50°C/W D1, D2 MOTOROLA SCHOTTKY VBR = 40V R3 KRL SP-1/2-A1-0R100J Pd = 0.75V L1 COILTRONICS CTX50-4 DCR = 0.175 IDC = 1.350A Kool M µ CORE


VOUT = 1.25V • (1 + R4/R5) = 12.3V FAST CHARGE = 120mV/R3 = 1.3A TRICKLE CHARGE = 100mA EFFICIENCY > 90%

ITH

CT

LTC1148HV

VIN

SENSE +

SENSE –

+

C6 0.01µF

C7 100pF

+

VIN 12V TO

18VC1 1µF

R2 1k

R1 51Ω

C4 3300pF X7R

C5 200pF NPO

10

0V = NORMAL > 1.5A = SHUTDOWN

4

1

8

7

9

14

Q1 Si9430DY

Q2 Si9410DY

D1 MBRS140T3

D2 MBRS340T3

C3 22µF × 2 35V

R3 0.1Ω

R4 442k 1%

VOUT

C8 100µF 16V × 2

3

11

12

Q3 VN2222LL

“1” TRICKLE CHARGE

SHUTDOWN

6

C2 0.1µF

+

L1 50µH1

2

4

3

AN54 • F33

SGND PGND

PDRIVE

VFB

NDRIVE

VBAT 6 CELLS

R5 49.9k 1%

Figure 33. LTC1148: High Voltage Charger Circuit

AN54-37

Application Note 54

LTC1142A: High Efficiency Power Supply Providing3.3V/2A with Built-In Battery Charger

Figure 34 implements a high efficiency step-down con-verter with a built-in battery charger using a single IC. Onesection of the dual LTC1142A is used to convert 4-cells to

3.3V/2A in a regular buck configuration. The other sectionis configured in the same way as the battery charger fromFigure 32. It is powered from a wall adapter and providesthe battery with fast or trickle charging rate. When theadapter is not connected, D3 prevents the battery fromdischarging through the R2/R1 divider network.

Figure 34. LTC1142A: High Efficiency Power Supply Providing 3.3V/2A with Built-In Battery Charger

1000pF

+

++

1000pF

PDRIVE1

SENSE+1

SENSE–1

NDRIVE1

PGND1 SGND1 CT1 ITH1 ITH2 CT2 SGND2 PGND2

NDRIVE2

SENSE–2

VFB2VFB1

SENSE+2

PDRIVE2

VIN1 SHUTDOWN 1 SHUTDOWN 2 VIN2

LTC1142A

CT2 330pF

5 4 25 27 13 11 18 19

RC2 1k

RX 51Ω

CC1 3300pF

CC2 3300pF

CT1 200pF

RC1 1k

0.22µF

324 17

100pF 100pF

10

9

15

14

16

20

23

1

28

2

6

VOUT2 3.3V/2A

VBATT 4 CELLS NiCAD

COUT2 220µF 10V × 2

RSENSE2 0.05Ω

P-CH Si9433DY

L2 25µH

D2 MBRS140T3

N-CH Si9410DY

0.22µF

CIN2 22µF 25V × 2

CIN1 22µF 35V × 2 P-CH

Si9430DY

N-CH Si9410DY

D1 MBRS140T3

D3 MBRS340T3

COUT1 220µF

10V

L1 50µH

RSENSE1 0.1Ω

R2 274k

1%

R4 84.5k 1%

R3 51k 1%

R1 49.9k

1%

VIN 8V TO 18V

FROM WALL ADAPTER0V = CHARGE ON

>1.5V = CHARGE OFF0V = OUTPUT ON

>1.5V = 3.3V OUTPUT OFF

L1 L2 RSENSE1 RSENSE2

COILTRONICS CTX50-4 COILTRONICS CTX25-4 KRL SL-C1-1/2-1R100J KRL SL-C1-1/2-1R050J

FAST CHARGE = 130mV/RSENSE1 = 1.3A TRICKLE CHARGE = 130mV/RSENSE1 = 100mA AN54 • F34

+

“1” FOR TRICKLE CHARGE

VN2222LL

Application Note 54

AN54-38

LTC1149: Dual Output Buck Converter

The circuit shown in Figure 35A implements the mostelegant approach for dual output regulators that provide3.3V and 5V outputs. It uses a single LTC1149. Thesynchronous rectification feature of this chip is used toprovide excellent efficiency, as well as good cross regula-tion between the two outputs. Maximum output power ofthe converter is 17W, which may be drawn in any combi-nation between 3.3V and 5V outputs.

A regular buck regulator is used for producing 3.3V outputwith T1’s primary in place of the buck inductor. Thesecondary of T1 forms a boost winding for 5V output. Thetransformer is wound with a simple trifilar winding toensure that the primary is closely coupled to the second-ary. Superior cross regulation is achieved by the closeprimary-to-secondary coupling and by splitting voltagefeedback paths (resistors R1 and R2 provide feedbacksignals from both 3.3V and 5V outputs). Diodes D1, D2and capacitor C7 comprise a soft-start circuit that causesthe output voltage to increase slowly when the power isfirst applied to the circuit. This circuit prevents overshoot

at the 3.3V output. The transformer used in this exampleis a standard product (see the parts list). A circuit boardhas been laid out for this circuit and has subsequentlybeen thoroughly tested under full operating conditionsand optimized for mass production requirements. A Ger-ber file for the board is available upon request.

Figure 35A. Single LTC1149: Dual Output Buck Converter

VINS/D1/VFB

S/D2

CT

ITH

VO(REG)

VI(REG)

CAP

PGATE

PDRIVE

NGATE

SENSE+

SENSE–

RGNDPGND SGND

LTC1149

10

15

6

7

3

5

16

C12 56pF

C13 2.2µF

12 14 11

1

4

13

9

8

R5 24.9k 1%

R4 1k

C8 0.068µF

C3, C4, C15, C16 C5, C6, C8, C17 R3 T1

AVX (Ta) TPSE227M010R 49BCPA AVX (Ta) TPSE226M035R 49BCPA IRC LR512-01-R020F HURRICANE, HL-8700

C10 2200pF

C11 1000pF

2

C19 0.1µF

D3 BAS16

C9 0.047µF

C14 1000pF

D1 BAS16

C7 10µF

QP1 Si9435DY

R6 100Ω

R7 100Ω

C20 1µF

4 QP2 Si9435DY

+

1

43

6

TP1

•

••

5

2

T1 HL-8700

–VIN

VIN 6V TO

24V +C5 22µF

+C6 22µF

+C17 22µF

+C18 22µF

R1 102k 1%

4

R8 33k

D6 BAS16

QN1 Si9410DY

D4 MBRS140

QN2 Si9410DY

+C1 220µF +C2

220µF

+C15 220µF +C16

220µF

+C3 220µF

D2 BAS16

R2 124k 1%

+C4 220µF

– VOUT

3.3V OUT

5V OUT

BOLD LINES INDICATE HIGH CURRENT PATHS (SHORT LEADS)

R3 0.02Ω

D5 MBRS140

AN54 • F35A

11 T11 T

11 T

Figure 35B. LTC1149: Dual Output Buck ConverterMeasured Efficiency

TOTAL POWER OUTPUT0

80

EFFI

CIEN

CY (%

)

82

86

88

90

100

94

4 8 10 18

AN54 • F35B

84

96

98

92

2 6 12 14 16

VIN = 6V

VIN = 20V

VIN = 12V

AN54-39

Application Note 54

LTC1148: Constant Frequency Buck Converters

Finally, Figures 36A and 37A show circuits that completelysatisfy the demand in ultra-high efficiency convertersoperating synchronously with an external clock. The risingedge of the clock saturates Q3 pulling pin 4 below theinternal comparator threshold. The internal logic assumesthe end of the off-time, and turns Q1 on. Now the LTC1148operates as a conventional constant frequency currentmode controller and therefore requires slope compensa-tion. Q2 generates an artificial ramp signal that is superim-posed on the inductor current waveform sensed by theshunt R7. This is a standard technique to eliminatesubharmonic oscillation, a phenomenon that occurs un-der simultaneous conditions of fixed frequency and fixedamplitude of inductor current when the duty cycle exceeds50%. Subharmonic oscillations are not related to theclosed-loop transfer function.

Figure 36B. LTC1148: (8V-15V to 5V/2A)Constant Frequency Buck ConverterMeasured Efficiency


EFFI

CIEN

CY (%

)

100

95

90

85

80

75

70

651 10

AN54 • F36B

VIN = 8V

VIN = 15V

AN54 • F36A

C8 1000pF

SLOPE COMPENSATION

Q1 Si9430DY

Q4 Si9410DY

C7 22µF 25V × 2

C9 220µF 10VC6

200pFC5

6800pF

10

6

4

11

1

8

7

14

12

3

U1

D3 MBR130T3

D2 1N4148

C7 AVX (Ta) TPSD226K025R0200 C9 AVX (Ta) TPSE227K010R0080 L1 COILTRONICS CTX15-4 R7 KRL SL-1-C1-0R040J PD = 1W

OPERATION BEYOND SPECIFIED INPUT VOLTAGE CAN CAUSE INSTABILITY. EXTERNAL OSCILLATOR INPUT: TTL LEVEL. FOR APPLICATIONS WITH VIN > 2VOUT SLOPE COMPENSATION CAN BE DELETED.

+

Q2 2N2222

D1 1N4148

D4 1N4148

LTC1148-5

VIN

SHUTDOWN

ITH

CT

SGND

PDRIVE

SENSE+

SENSE–

NDRIVE

PGND

L1 15µH

R3 220Ω

R5 750Ω

R8 100Ω

R7 0.04Ω

R9 100Ω

R4 100Ω

C4 51pF

Q3 2N2222

R10 510k

+

+

C2 0.1µF

C3 1µF

C1 100pF

R6 1k

R1 30k

> 1.5V = SHUTDOWN

OSC IN 200kHz R2

5.1k

VOUT 5V 2A

VIN 8V TO 15V

Figure 36A. LTC1148: (8V-15V to 5V/2A) Constant Frequency Buck Converter

Application Note 54

AN54-40

If the input voltage always exceeds twice the output (dutycycle in this case would be less than 50%) the circuit insidethe dashed box can be omitted. Resistor R11 is added tothe circuit of disable Burst Mode operation ensuring truein-sync operation over the full range of output current. Thecircuitry is designed to be synchronized by a 200kHzclock to accommodate other external frequencies; nothingmore than component value changes is required. If theinput voltage goes beyond specified range, the controllerwill lose synchronization (it will still regulate, however).R10 increases input voltage pull-in range and can beomitted if it is not required. Values above 430k ensureproper start-up.


EFFI

CIEN

CY (%

)

100

95

90

85

80

75

70

651 10

AN54 • F37B

4.5V TO 3.3V/2A

6.5V TO 3.3V/2A

Figure 37B. LTC1148: (4.5V-6.5V to 3.3V/2A)Constant Frequency Buck ConverterMeasured Efficiency

Figure 37A. LTC1148: (4.5V-6.5V to 3.3V/2A) Constant Frequency Buck Converter

AN54 • F37A

C8 1000pF

SLOPE COMPENSATION

Q1 Si9430DY

Q4 Si9410DY

C7 22µF 25V × 2

C9 220µF 10VC6

150pFC5

3300pF

10

6

4

11

1

8

7

14

12

3

U1

D3 MBR130T3

D2 1N4148

C7 AVX (Ta) TPSD226K025R0200 C9 AVX (Ta) TPSE227K010R0080 L1 COILTRONICS CTX15-4 R7 KRL SL-1-C1-R040J PD = 1W

OPERATION BEYOND SPECIFIED INPUT VOLTAGE CAN CAUSE INSTABILITY. EXTERNAL OSCILLATOR INPUT: TTL LEVEL.

+

Q2 2N2222

D1 1N4148

D4 1N4148

LTC1148-3.3

VIN

SHUTDOWN

ITH

CT

SGND

PDRIVE

SENSE+

SENSE–

NDRIVE

PGND

L1 15µH

R5 750Ω

R8 100Ω

R7 0.04Ω

R9 100Ω

R4 100Ω

C4 50pF

Q3 2N2222

R10 470k

+

+

C2 0.1µF

C3 1µF

C1 100pF

R6 100Ω

R1 20k

> 1.5V = SHUTDOWN

OSC IN 200kHz R2

2.2k

VOUT 3.3V 2A

VIN 4.5V TO 6.5V

R11 18k

AN54-41

Application Note 54

APPENDIX A

TOPICS OF COMMON INTEREST

Defeating Bust Mode Operation

Sometimes applications require Burst Mode operation tobe defeated. It might be useful in a high output currentcircuit which never operates at light loads. Ensuringcontinuous operation in this case usually improves thecircuit noise immunity and helps to eliminate audible noisefrom certain types of inductors when they are lighterloaded. The Burst Mode operation should be disabled if anoverwinding is used to provide boosted voltage, additionalto the main output (for example, see Figure 30A). Thisallows to draw power from the secondary with improvedcross-regulation, even if the primary output is not loaded.Defeating of Burst Mode operation should also be consid-ered when the fixed frequency circuits from Figures 36Aand 37A are used. With continuous operation these cir-cuits always operate fully synchronized to the externalclock.

Whatever the reason, Burst Mode operation can be sup-pressed with a simple external network which cancels the25mV minimum current comparator threshold. An exter-nal offset is put in series with the SENSE – pin to subtractfrom the built-in 25mV offset. An example of this tech-nique is shown in Figure A1.

LTC1148 FAMILY R2

100Ω

L 33µH

R1 100ΩR3

20k

SENSE+

100pF

SENSE–

RSENSE 0.05Ω VOUT

5V 2A

AN54 • FA01

Two 100Ω resistors are inserted in series with the leadsfrom the sense resistor. With the addition of R3, a currentis generated through R1 causing an offset of:

V VR

R ROFFSET OUT= ×+

11 3

If VOFFSET exceeds 25mV the minimum threshold will becancelled and Burst Mode operation is prevented fromoccurring. Since the offset voltage is constant, the maxi-mum load current is also decreased. Thus to get back tothe same output current, the sense resistor must be lower:

RmV

ISENSEMAX

= 75

Soft-Start Circuits

Right after the power-on, the regulator operates in a short-circuit condition while charging output capacitors. Withearlier voltage mode converters, this led to enormouscurrent transient at start-up. Soft-start circuits were usu-ally added to fix this problem. The LTC1148 seriesimplements current mode technique which inherentlyprovides current limiting and does not require any specialsoft-start circuits. Start-up current is limited to the short-circuit current value of 150mV/RSENSE.

Some applications might, however, require softer start. Ithelps to avoid output overshoot when the power is firstapplied to the circuit, and it also prevents the inputsupply’s overcurrent protection from latching, when theinput voltage increases slowly. Figures A2 and A3 providepossible solutions for soft-start. Capacitor C1 in Figure A2holds down ITH pin limiting the output current. C1 ischarged via R1, when the voltage across its terminalsexceeds DC level of ITH pin, D2 becomes reverse-biasedand the capacitor no longer has an effect on the circuitoperation. D1 provides discharge path for C1 when theinput voltage is removed. The soft-start time constant isdefined by R1 and C1.

In Figure A3, capacitor C1 holds down the SENSE– pinproviding additional offset to the current comparator. C1charges through D1 and R2, slowly increasing maximumoperating current. When C1 is fully charged D1 is reverse-biased and the capacitor no longer affects the operation.

Figure A1. Defeating Burst Mode

Application Note 54

AN54-42

D2 provides a discharge path for C1 when the outputvoltage disappears. The soft-start time constant is definedby R2 and C1.

LTC1148 FAMILY

R2 1k

D2 MBR0520L

VIN

ITH

C2 3300pF

C1 4.7µF

16V

VIN

AN54 • FA02

R1 22k

D1 1N4148

+

Figure A2. Soft-Start Circuit with ITH Pin Clamping

Figure A3. Soft-Start Circuit with Sense Pin Clamping

LTC1148 FAMILY R1

100Ω

L 33µH

R2 100Ω

SENSE+

C2 1000pF

D1 1N4148

D2 1N4148

C1 10µF 10V

SENSE–

RSENSE 0.05Ω VOUT

5V 2A

AN54 • FA03

+

Frequency Compensation

The LTC1148 family of regulators contains both voltageand current loops, which, together with external capaci-tors and inductors, require a pretty complex mathematicalapproach to frequency compensation. Operating pointchanges with input voltage and output current variationsadd complications and suggest a more practical empiricalmethod.

The simplest approach uses load step transient by switch-ing in an additional load resistor and simultaneouslymonitoring the output. Switching regulators take severalcycles to respond to a step in resistive load current. Whena load step occurs, output voltage shifts by an amountequal to ∆ILOAD × ESR, where ESR is the output capacitoreffective series resistance. Load current change also be-gins to charge or discharge output capacitor until theregulator loop adapts to the current change and returnsVOUT to its steady state value. If during this recovery timeVOUT has ringing, it indicates a stability problem, and thecapacitor at ITH pin should be increased.

A simple dynamic load circuit is shown in Figure A4 wherethe MOSFET Q1, driven by an external generator, switchesa load resistor R2 in and out. The generator should provide10V gate drive (not a TTL level). The drive signal frequencyis not critical. A good starting point is 500Hz and the loadchange from 50% to the full load.

Figure A4. Simple Dynamic Load

The LTC1148 series regulators provide a very stableoperation. The compensation values used in the circuits inthis note have been tested over the wide range of operatingconditions and proved to provide an adequate compensa-tion for most applications. Usually no stability testing, asdescribed above, is required.

LTC1148 FAMILY

GENERATOR IN (10VP-P)

Q1 IRFZ44

(HEAD SINK MAY BE REQUIRED)

R1 R2COUT

AN54 • FA04

100k

+

AN54-43

Application Note 54

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen-tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.

APPENDIX B

SUGGESTED MANUFACTURERS

Linear Technology provides this list of manufacturers toget you started in your component selection process. Wemake no claims about any of these companies except thatthey provide components necessary in switching powersupplies. There are many more companies to choosefrom; for a more complete list refer to the PCIM Buyer’s

Guide. PCIM (Power Conversion & Intelligent Motion) ispublished by Intertec International Inc., 2472 EastmanAve., Bldg. 33-34, Ventura, California 93003-5774, (805)650-7070. PCIM is free to qualified applicants. Backissues, such as the Buyer’s Guide can be purchased.

Philips Components1440 W. Indian Town Rd.Jupiter, FL 33458(407) 744-4200Cer., Chip Capacitors

Murata Erie North America1900 W. College Ave.State College, PA 16801(814) 237-1431

Nichicon (America) Corporation927 East State ParkwaySchaumburg, IL 60173(708) 843-7500Aluminum Electrolytic

Sanyo Video Components (USA) Corp.2001 Sanyo Ave.San Diego, CA 92173(619) 661-6835Low ESR Filter Capacitors-Solid AluminumElectrolytic Capacitors (OS-CON)

Sprague678 Main St.P.O. Box 231Sanford, ME 04073(207) 324-4140Tantalum Capacitors

Current Sense ResistorsDale Electronics1122 23rd St.P.O.Box 609Columbus, NE 68602(402) 564-3131Resistors, Inductors, Xformers

IRC4222 South Staples St.Corpus Christi, TX 78411(512) 992-7900

KRL160 Bouchard St.Manchester, NH 03103(603) 668-3210

DiodesFuji/Collmer14368 Proton Rd.Dallas, TX 75244(214) 233-1589Low Current Schottkys

General Instruments10 Melville Park Rd.Melville, NY 11747(516) 847-3222

Motorola Inc.5005 E. McDowell Rd.P.O. Box 2953Phoenix, AZ 85062(602) 244-5768Diodes

Philips Components Disc. Prod. Div.100 Providence PikeSlatersville, RI 02876(401) 762-3800Discrete Semi Group

Ferrite BeadsFair-Rite Products Corp.1 Commerial RowP.O. Box JWallkill, NY 12589(914) 895-2055

Toshiba America Elec. Components9775 Toledo WayIrvine, CA 92718(714) 455-2000

Heat SinksAavid Engineering, Inc.One Kool Path Box 400Laconia, NH 03247(603) 528-3400

Int’l Electronic Research Group135 W. Magnolia Blvd.Burbank, CA 91502(213) 849-2481

BatteriesDuracellOEM Sales & MarketingBerkshire Industrial ParkBethel, CT 06801(800) 431-2656

Eveready Battery Co.Checkerboard SquareSt. Louis, MO 63164(314) 982-2000

Bipolar TransistorsMotorola Inc.3102 North 56th St.MS 56-126Phoenix, AZ 85018(800) 521-6274Full Line

Zetex87 Modular Ave.Commack, NY 11725(516) 543-7100High Gain Bipolar Switching Transistorsincluding Surface Mount Devices

CapacitorsAVX CorporationP.O. Box 867Myrtle Beach, SC 29578(803) 946-0690Tant., Cer., Surface Mount

Elpac1567 Reynolds Ave.Irvine, CA 92714Film Capacitors(714) 476-6070Film Capacitors

Intertechnical Group2269 Saw Mill River Rd., Bldg. 4CP.O. Box 217Elmsford, NY 10523(914) 347-2474Polycarbonate Film

Application Note 54

AN54-44 LINEAR TECHNOLOGY CORPORATION 1993

LT/GP 1094 5K REV A • PRINTED IN USALinear Technology Corporation1630 McCarthy Blvd., Milpitas, CA 95035-7487(408) 432-1900 FAX: (408) 434-0507 TELEX: 499-3977

Thermalloy2021 W. Valley View LaneDallas, TX 75234(214) 243-4321

Inductors and TransformersBeckman Industrial Corp.4200 Bonita PlaceFullerton, CA 92635(714) 447-2345Inductors, Xformers including SMT

Caddell-Burns258 East Second St.Mineola, NY 11501(516) 746-2310

Coilcraft1102 Silver Lake Rd.Cary, IL 60013(800) 322-2645

Coiltronics6000 Park of Commerce Blvd.Boca Raton, FL 33487(407) 241-7876Full Line including Surface Mount Inductors

Dale ElectronicsE. Highway 50P. O. Box 180Yankton, SD 57078(605) 665-9301Inductors, Xformers including SMT

Gowanda Electronics Corp.1 Industrial PlaceGowanda, NY 14070(716) 532-2234

Hurricane Electronics LabP.O. Box 1280Hurricane, UT 84737(801) 635-2003

Murata Erie North America2200 Lake Park DriveSmyrna, GA 30080(404) 436-1300

Renco60 E. Jefryn Blvd.Deerpark, NY 11729(516) 586-5566

Sumida Electronic5999 New Wilke Rd., Ste. 110Rolling Meadows, IL 60008(708) 956-0666

TDK Corp. of America1600 Feehanville Dr.Mount Prospect, IL 60056(708) 803-6100

Thermalloy2021 W. Valley View LaneDallas, TX 75234(214) 243-4321Power Sockets, Thermal Compounds,and Adhesives Thermally ConductiveInsulators, Mounting Kits

Power MOSFETsInternational Rectifier Corp.233 Kansas St.El Segundo, CA 90245(310) 322-3331

Motorola Inc.5005 E. McDowell Rd.Phoenix, AZ 85008(602) 244-3576

Siliconix2201 Laurelwood Rd.Santa Clara, CA 96056(800) 554-5565

ResistorsMicro-Ohm Corp.1088 Hamilton Rd.Duarte, CA 91010(818) 357-5377

Thermo Disc1981 Port City Blvd.Muskegon, MI 49443(616) 777-2602

RCD Components, Inc.520 East Industrial Park Dr.Manchester, NH 03109(603) 669-0054

Caddock Electronics1717 Chicago Ave.Riverside, CA 92507-2364(909) 788-1700

WireBelden Wire & CableP.O. BOX 1980Richmond, IN 47375(317) 983-5200

Toko America Incorporated1250 Feehanville Dr.Mount Propsect, IL 60056(708) 635-3200

Magnetic MaterialsFair-Rite Products Corp.1 Commercial RowP. O. Box JWallkill, NY 12589(914) 895-2055Ferrite

Micrometals, Inc.1190 N. Hawk CircleAnaheim, CA 92807(800) 356-5977Powdered Iron

Magnetics Div. Spang & CoP.O. Box 391Butler, PA 16003-0391(412) 282-8282Molypermalloy, Kool Mµ, Ferrite

Philips Components Disc. Prod. Div.Materials Group1033 King HighwaySaugerties, NY 12477(914) 246-2811Ferrite

Pyroferric International, Inc.200 Madison St.Toledo, IL 62468(217) 849-3300Powdered Iron

Siemens Components, Inc.186 Wood Ave. SouthIselin, NJ 08830(908) 906-4300Ferrite

TDK Corp. of America1600 Feehanville Dr.Mount Prospect, IL 60056(708) 803-6100Ferrite

Mounting HardwareBergquist5300 Edina Industrial Blvd.Minneapolis, MN 55439(612) 835-2322Thermally Conductive Insulators

Stockwell Rubber4749 Tolbut St.Philadelphia, PA 19136(800) 523-0123Thermally Conductive Insulators

Power Conversion from Milliamps to Amps at Ultra-High Efficiency

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