IRDC3846-P0V9

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USER GUIDE FOR IRDC3846 EVALUATION BOARD

DESCRIPTION

The IR3846 is a synchronous buckconverter, providing a compact, highperformance and flexible solution in a small5mmx7mm QFN package.

Key features offered by the IR3846 includeinternal Digital Soft Start, precision 0.6Vreference voltage, Power Good, thermalprotection, programmable switchingfrequency, Enable input, input under-voltagelockout for proper start-up, enhanced line/load regulation with feed forward, externalfrequency synchronization with smoothclocking, internal LDO, true differentialremote sensing and pre-bias start-up.

A thermally compensated output over-currentprotection function is implemented by sensingthe voltage developed across the on-resistanceof the synchronous rectifier MOSFET foroptimum cost and performance.

This user guide contains the schematic and billof materials for the IRDC3846 evaluation board.The guide describes operation and use of theevaluation board itself. Detailed applicationinformation for IR3846 is available in theIR3846 data sheet.

BOARD FEATURES

• Vin = +12V, No Vcc required.

• Vout = +0.9V @ 0-25A

• Fs=400kHz

• L= 0.330uH

• Cin= 7x22uF (ceramic 1206) + 1x330uF (electrolytic)

• Cout= 8x22uF (ceramic 0805) + 4x470uF (SP-Cap)

SupIRBuckTM

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A well regulated +12V input supply should be connected to VIN+ and VIN-. A maximum of 25A load shouldbe connected to VOUT+ and VOUT-. The inputs and output connections of the board are listed in Table I.

IR3846 needs only one input supply and internal LDO generates Vcc from Vin. If operation with external Vccis required, then R3 should be removed and external Vcc can be applied between Vcc+ and Vcc- pins. Vinpin and Vcc pins should be shorted together for external Vcc operation by installing a 0 ohm resistor at R4.

The board is configured for remote sensing. If local sense is desired, R18 should be uninstalled and R19should be installed instead.

External Enable signal can be applied to the board via exposed Enable pad and R100 should be removedfor this purpose.

CONNECTIONS and OPERATING INSTRUCTIONS

LAYOUTThe PCB is a 6-layer board. All of layers are 2 Oz. copper. The IR3846 and most of the passivecomponents are mounted on the top side of the board.

Power supply decoupling capacitors and feedback components are located close to IR3846. Thefeedback resistors are connected to the output of the remote sense amplifier of the IR3846 and arelocated close to the IR3846. To improve efficiency, the circuit board is designed to minimize the length

of the on-board power ground current path. Separate power ground and analog ground are used andmay be connected together using a 0 ohm resistor at R71.

Table I. Connections

Connection Signal Name

VIN+ Vin (+12V)

VIN- Ground of Vin

Vout+ Vout(+0.9V)

Vout- Ground for Vout

Vcc+ Vcc Pin

Vcc- Ground for Vcc input

Enable Enable

PGood Power Good Signal

AGnd Analog ground

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CONNECTIONS and OPERATING INSTRUCTIONS

LAYOUTThe PCB is a 6-layer board. All of layers are 2 Oz. copper. The IR3846 and most of the passivecomponents are mounted on the top side of the board.

Power supply decoupling capacitors and feedback components are located close to IR3846. Thefeedback resistors are connected to the output of the remote sense amplifier of the IR3846 and arelocated close to the IR3846. To improve efficiency, the circuit board is designed to minimize the length

of the on-board power ground current path. Separate power ground and analog ground are used andmay be connected together using a 0 ohm resistor at R71.

Vin VoGnd Gnd

Top View

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Fig

.1:

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ico

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3846

eval

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po

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Sig

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( “

anal

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Gro

un

d

Vre

f

S_

Ctr

l

1

C13

0

N/S

R11

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M2

N/S

R11

3

N/S

BO

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MP

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2

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330nH

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R70

N/S

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Vin 1

C16

N/S

R11

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23

4

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C1

19

N/S

C12

0

N/S

C12

1

N/S

C12

2

N/S

Option

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as t

est

circ

uit

C12

3

N/S

FB

C14

N/S

C12

4

N/S

Sy

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R1

01

C11

3.6n

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VP

B

1

R114

N/S

R10

17.

5K

SW 1

C77

22uF

R11

8.2

5K

C79

N/S

R19

N/S

R12

1.3

7K

R13

10.5

K

C78

N/S

C11

4

N/S

R1

520

Vs

ns

PVin

C1

13

N/S

R48

N/S

C10

8

N/S

C10

7

N/S

R49

N/S

C10

6

N/S

PG

D

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IR38

46

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BO

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4

NC

322

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7

NC

12

RS+16

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Comp10

PGND12

LGND13

FB9

VC

C21

NC

423

Vin

20

SW

24

S_Ctrl14

RS-15

NC

23

PG

D19

NC526

R11

50

C10

5

N/S

+C

125

470u

F

PV

in

C73

22uF

C70

0.1

uF

C7

22

2uF

BO

DE

2

JUM

PE

R 3

C71

22uF

C7

62

2uF

7 x 22uF / 1206 / 25V / Ceramic Capacitor

8 x 22uF / 0805 / 6.3V / Ceramic Capacitor

330uF / 25V / Electrolytic Capacitor

+C

126

470

uF

BO

OT

R17

21K

Vcc

-1

+C

127

N/S

D2

N/S1

2

D1

N/S

1 2

Vsns

R10

049

.9K

+C

81

330

uF

+C

128

470u

F

R3

0

PV

in

4 x 470uF / 2.5V / SP-Cap

C11

5

N/S

C10

4

22u

F

No Jumper [Float]

PG_PU

VCC

C1

12

22uF

C13

2200

pFC74

22u

F

Rt/

Sy

nc

R9

60.4

K

C8

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C1

5N

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+C

129

470

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R16

10.5

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C8

10uF

C6

1uF

Vin

Agn

d1

C10

3

22uF

Vo

ut

R11

80

R11

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C10

2

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1

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1

22uF

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R_

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R14

21K

C71-C80: 0805 / 1206 pads

R46-R49: 1206 pads

C100-C124: 0805 / 1206 pads

C19

N/S

R71

0

R47

0

VC

C

C10

9

22u

F

Vou

t-123456

Vin

R46

0

Vcc

+1

FB

PG

ood

1

Vo

ut_

Adj

1

C1

239

pF

R4

N/S

R40

N/S

R41

N/S

Vo_

R_N

C40

N/S

C11

0

22u

F

R111

10K

FB

C5

N/S

C17

100

pF

Vre

f

Vin 1

Vre

f

1

Vin

C75

22uF

R18

0

C11

1

22u

F

VC

C

VC

CC

116

N/S

Sy

nc 1

Ena

ble

1

BO

OT

R110

10K

C11

7

N/S

C10

0.1

uF

Vp

C11

8

N/S

Vin

+

123456

Vin

-

123456

Vin 1

Vp 1

Vin 1

VD

DQ

1

Vin 1

C10

0

N/S

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Schematic for Transient Load set up

N/S

R33N/S

VoutC30N/S

R34N/S

R35N/S

R36N/S

R37N/S

ExtLoadCtrl

1

M1IRF6721 N/S

U2

MIC4452/SO8 N/S

VS1

IN2

GND4

GND5OUT16OUT27VS8

N/A3

R30N/S

R32N/S

S3SW

213

C330.1uF

C31N/S

R31N/S

Vout

C32N/S

Vo_R_P

D4N/S

D3N/S

R38N/S

R39N/S

Vo_R_N

Optional transient load circuit

VCC

I-Monitor1

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Bill of MaterialsItem Qty Part Reference Value Description Manufacturer Part Number

1 7C71 C72 C73 C74 C75 C76

C7722uF 1206, 25V, X5R, 10% Murata GRM31CR61E226KE15L

2 1 C6 1uF 0603, X5R, 25V, 20% TDK C1608X5R1E105M3 1 C8 10uF 0603, X5R, 10V, 20% TDK C1608X5R1A106M4 3 C10 C70 C130 0.1uF 0603, 25V, X7R, 10% Murata GRM188R71E104KA01D5 1 C11 3600pF 0603, 50V, NP0, 5% Murata GRM1885C1H362JA01D6 1 C12 39pF 0603, 50V, NP0, 5% Murata GRM1885C1H390JA01D7 1 C13 2200pF 0603, 50V, X7R, 10% Murata GRM188R71H222KA01D8 1 C17 100pF 0603, 50V, C0G, 5% Murata GRM1885C1H101JA01D

9 1 C81 330uFSMD Elecrolytic, Fsize,

25V, 20%Panasonic EEV-FK1E331P

10 1 L1 330nH330nH,

DCR=0.165mohmWurth

Electronics Inc.744309033

11 8C101 C102 C103 C104 C109 C110

C111 C11222uF 0805, 6.3V, X5R, 20% TDK C2012X5R0J226M

12 4C125 C126 C128 C129

470uFSP-Cap, 2.5V,

ESR=6mΩ, 20%Panasonic EEFLX0E471R

13 5R3 R18 R115 R116 R118

0 0603,1/10W, Jumper Vishay/Dale CRCW06030000Z0EA

14 1 R9 60.4K 0603,1/10W,1% Panasonic ERJ-3EKF6042V15 1 R10 1 0603,1/10W,5% Panasonic ERJ-3GEYJ1R0V16 1 R11 8.25K 0603,1/10W,1% Panasonic ERJ-3EKF8251V17 1 R12 1.37K 0603,1/10W,1% Panasonic ERJ-3EKF1371V18 2 R13 R16 10.5K 0603,1/10W,1% Panasonic ERJ-3EKF1052V19 2 R14 R17 21K 0603,1/10W,1% Panasonic ERJ-3EKF2102V20 1 R15 20 0603,1/10W,1% Vishay/Dale CRCW060320R0FKEA21 2 R46 R47 0 1206,1/4W, Jumper Yageo RC1206JR-070RL22 1 R71 0 0402, 1/16W, Jumper Yageo RC0402JR-070RL23 1 R100 49.9K 0603,1/10 W,1% Panasonic ERJ-3EKF4992V24 1 R101 7.5K 0603,1/10W,1% Panasonic ERJ-3EKF7501V25 2 R110 R111 10K 0603,1/10 W,1% Panasonic ERJ-3EKF1002V

26 1 JumperPLUG 40 POS DBL

ROW STROmron

Electronics Inc.XG8W-4041-ND

27 2 Vin+ Vout+ RED SCREW TERMINALKeystone

Electronics8199-2

28 2 Vin- Vout- BLACK SCREW TERMINALKeystone

Electronics8199-3

29 1 U1 IR3846 IR3846 5mm X 7mmInternational

RectifierIR3846MPBF

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Fig. 5: Output Voltage Ripple, 25A load Ch1: Vo

Fig. 6: Inductor node at 25A loadCh2:LX

Fig. 7: Short (Hiccup) RecoveryCh2:Vo, Ch3:PGood, Ch4:Io

Fig. 3: Start up at 25A Load Ch1:Vin, Ch2:Vo, Ch3:PGood, Ch4:Vcc

Fig. 2: Start up at 25A LoadCh1:Vin, Ch2:Vo, Ch3:PGood, Ch4:Enable

Fig. 4: Start up with 0.8V Pre Bias, 0A Load Ch1:Enable,Ch2:Vo, Ch3:PGood

TYPICAL OPERATING WAVEFORMSVin=12.0V, Vo=0.9V, Io=0A-25A, Fsw=400kHz, Room Temperature, No air flow

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TYPICAL OPERATING WAVEFORMSVin=12.0V, Vo=0.9V, Io=2A-14.5A, Fsw=400kHz, Room Temperature, No air flow

Fig. 8: Transient Response, 2A to 14.5A step (2.5A/us)Ch2:Vout, Ch4:Iout

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TYPICAL OPERATING WAVEFORMSVin=12.0V, Vo=0.9V, Io=12.5A-25.0A, Fsw=400kHz, Room Temperature, No air flow

Fig. 9: Transient Response, 12.5A to 25A step (2.5A/us)Ch2:Vo, Ch4:Io

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TYPICAL OPERATING WAVEFORMSVin=12.0V, Vo=0.9V, Io=25A, Fsw=400kHz, Room Temperature, No air flow

Fig. 10: Bode Plot at 25A load: Fo = 38.6kHz; Phase Margin = 57.4º; Gain Margin = -20.7dB

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Fig.12: Power loss versus load current

Fig.11: Efficiency versus load current

TYPICAL OPERATING WAVEFORMSVin=12.0V, Vo=0.9V, Io=0A-25A, Fsw=400kHz, Room Temperature, No air flow

727374757677787980818283848586878889909192

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Eff

icie

ncy

[%

]

Io [A]

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Po

wer

Lo

ss [

W]

Io [A]

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Fig. 13: Thermal Image of the board at 25A loadIR3846: 69.00CInductor: 58.40CAmbient: 27.10C

TYPICAL OPERATING WAVEFORMSVin=12.0V, Vo=0.9V, Io=25A, Fsw=400kHz, Room Temperature, No air flow

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IR WORLD HEADQUARTERS: 233 Kansas St., El Segundo, California 90245, USA Tel: (310) 252-7105

TAC Fax: (310) 252-7903Visit us at www.irf.com for sales contact information

Data and specifications subject to change without notice.