uc3854a
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6/98 BLOCK DIAGRAM • Controls Boost PWM to Near Unity Power Factor • Limits Line Current Distortion To <3% • World-Wide Operation Without Switches • Accurate Power Limiting • Fixed Frequency Average Current Mode Control • High Bandwidth (5MHz), Low Offset Current Amplifier • Integrated Current and Voltage Amp Output Clamps • Multiplier Improvements: Linearity, 500mV VAC Offset (eliminates external resistor), 0-5V Multout Common Mode Range • VREF "GOOD" Comparator • Faster and Improved Accuracy ENABLE Comparator • UVLO Threshold Options (16/10V / 10.5/10V) • 300μA Startup Supply Current The UC1854A/B products are pin compatible enhanced versions of the UC1854. Like the UC1854, these products provide all of the functions necessary for active power factor corrected preregulators. The controller achieves near unity power factor by shaping the AC input line current waveform to correspond to the AC input line voltage. To do this the UC1854A/B uses average current mode control. Average current mode control maintains stable, low distortion sinusoidal line current without the need for slope compensation, unlike peak current mode control. The UC1854A/B products improve upon the UC1854 by offering a wide bandwidth, low offset Current Amplifier, a faster responding and improved accuracy enable comparator, a VREF "good" comparator, UVLO threshold options (16/10V for offline, 10.5/10V for startup from an auxiliary 12V regulator), lower startup supply current, and an enhanced multiply/divide circuit. New features like the amplifier output clamps, improved amplifier current sinking capability, and low offset VAC pin reduce the external component count while improving performance. Improved common mode input range of the Multiplier output/Current Amp input allow the designer greater flexibility in choosing a method for current sensing. Unlike its predecessor, RSET controls only oscillator charging current and has no effect on clamping the maximum multiplier output current. This current is now clamped to a maximum of 2 * I AC at all times which simplifies the design process and provides foldback power limiting during brownout and extreme low line conditions. A 1% 7.5V reference, fixed frequency oscillator, PWM, Voltage Amplifier with softstart, line voltage feedforward (VRMS squarer), input supply voltage clamp, and over current comparator round out the list of features. UC1854A/B UC2854A/B UC3854A/B Enhanced High Power Factor Preregulator FEATURES DESCRIPTION UVLO Turn on UVLO Turn off UC1854A 16V 10V UC1854B 10.5V 10V UDG-93001-1
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Transcript of uc3854a
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6/98
BLOCK DIAGRAM
Controls Boost PWM to Near UnityPower Factor
Limits Line Current Distortion To
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DIL16 & SOIC-16(Top View)J, N & DW Packages
PACKAGE PIN FUNCTIONFUNCTION PIN
N/C 1 Gnd 2PKLMT 3CA Out 4ISENSE 5N/C 6Mult Out 7IAC 8VA Out 9VRMS 10N/C 11VREF 12ENA 13VSENSE 14RSET 15N/C 16SS 17CT 18VCC 19GT Drv 20
PLCC-20 & LCC-20(Top View)Q & L Packages
CONNECTION DIAGRAMS
Supply Voltage VCC . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22VGT Drv Current, Continuous. . . . . . . . . . . . . . . . . . . . . . . 0.5AGT Drv Current, 50% Duty Cycle. . . . . . . . . . . . . . . . . . . . 1.5AInput Voltage, VSENSE, VRMS . . . . . . . . . . . . . . . . . . . . . . . 11VInput Voltage, ISENSE, Mult Out . . . . . . . . . . . . . . . . . . . . . 11VInput Voltage, PKLMT . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5VInput Current, RSET, IAC, PKLMT, ENA . . . . . . . . . . . . . . 10mAPower Dissipation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1W Storage Temperature . . . . . . . . . . . . . . . 65C to +150CLead Temperature (Soldering, 10 Seconds) . . . . . . . . . +300C
ABSOLUTE MAXIMUM RATINGS
UC1854A/BUC2854A/BUC3854A/B
Note 1: All voltages with respect to Gnd (Pin 1).Note 2: All currents are positive into the specified terminal.Note 3: ENA imput is internally clamped to approximately 10V.Note 4: Consult Unitrode Integrated Circuits databook forinformation regarding thermal specifications and limitations ofpackages.
PARAMETER TEST CONDITIONS MIN TYP MAX UNITSOVERALL
Supply Current, Off CAO, VAO = 0V, VCC = UVLO - 0.3V 250 400 ASupply Current, On 12 18 mAVCC Turn-On Threshold UC1854A 16 17.5 V
UC1854B 10.5 11.2 VVCC Turn-Off Threshold UC1854A / B 9 10 VVCC Clamp I(VCC) = ICC(on) + 5mA 18 20 22 V
VOLTAGE AMPLIFIERInput Voltage 2.9 3.0 3.1 VVSENSE Bias Current 500 25 500 nAOpen Loop Gain VOUT = 2 to 5V 70 100 dBVOUT High ILOAD = 500A 6 VVOUT Low ILOAD = 500A 0.3 0.5 VOutput Short Circuit Current VOUT = 0V 1.5 3.5 mAGain Bandwidth Product Fin = 100kHz, 10mV p-p, (Note 1) 1 mHz
Unless otherwise stated, VCC=18V, RT=8.2k, CT=1.5nF, PKLMT=1V, VRMS=1.5V,IAC=100A, ISENSE=0V, CA Out=3.5V, VA Out=5V, VSENSE=3V, 55oC
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ELECTRICALCHARACTERISTICS (cont.)
PARAMETER TEST CONDITIONS MIN TYP MAX UNITSCURRENT AMPLIFIER
Input Offset Voltage VCM = 0V TA = +25C 4 0 mVOverTemp 5.5 0 mV
Input Bias Current(sense) VCM = 0V 500 500 nAOpen Loop Gain VCM = 0V, VOUT = 2 to 6V 80 110 dBVOUT High ILOAD = 500A 8 VVOUT Low ILOAD = 500A 0.3 0.5 VOutput Short Circuit Current VOUT = 0V 1.5 3.5 mACommon Mode Range 0.3 5 VGain Bandwidth Product Fin = 100kHz, 10mV p-p, (Note 1) 3 5 mHz
REFERENCEOutput Voltage IREF = 0mA, TA = 25oC 7.4 7.5 7.6 V
IREF = 0mA 7.35 7.5 7.65 VLoad Regulation IREF = 1 to 10mA 0 8 20 mVLine Regulation VCC = 12 to 18V 0 14 25 mVShort Circuit Current VREF = 0V 25 35 60 mA
OSCILLATORInitial Accuracy TA = 25oC 85 100 115 kHzVoltage Stability VCC = 12 to 18V 1 %Total Variation Line, Temp 80 120 kHzRamp Amplitude (p-p) 4.9 5.9 VRamp Valley Voltage 0.8 1.3 V
ENABLE / SOFTSTART / CURRENT LIMITEnable Threshold 2.35 2.55 2.8 VEnable Hysteresis VFAULT = 2.5V 500 600 mVEnable Input Bias Current VENABLE = 0V 2 5 APropagation Delay to Disable Enable Overdrive = 100mV,(Note 1) 300 nsSS Charge Current VSOFTSTART = 2.5V 10 14 24PKLMT Offset Voltage 15 15 mVPKLMT Input Current VPKLMT = 0.1V 200 100 APKLMT Propagation Delay (Note 1) 150 ns
MULTIPLIEROutput Current - IAC Limited IAC=100A, VRMS = 1V, RSET = 10k 220 200 170 AOutput Current - Zero IAC=0A, RSET = 10k 2.0 0.2 2.0 AOutput Current - Power Limited VRMS = 1.5V, Va = 6V 230 200 170 AOutput Current VRMS = 1.5V, Va = 2V 22 A
VRMS = 1.5V, Va = 5V 156 AVRMS = 5V, Va = 2V 2 AVRMS = 5V, Va = 5V 14 A
Gain Constant (Note 2) VRMS = 1.5V, TJ = 25C, Va = 6V 1.1 1.0 0.9 A/A
UC1854A/BUC2854A/BUC3854A/B
Unless otherwise stated, VCC=18V, RT=8.2k, CT=1.5nF, PKLMT=1V, VRMS=1.5V,IAC=100A, ISENSE=0V, CA Out=3.5V, VA Out=5V, VSENSE=3V, 55oC
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PARAMETER TEST CONDITIONS MIN TYP MAX UNITSGATE DRIVER
Output High Voltage IOUT = 200mA, VCC = 15V 12 12.8 VOutput Low Voltage IOUT = 200mA 1 2.2 V
IOUT = 10mA 300 500 mVOutput Low (UVLO) IOUT = 50mA, VCC = 0V 0.9 1.5 VOutput Rise / Fall Time CLOAD = 1nF, (Note 1) 35 nsOutput Peak Current CLOAD = 10nF, (Note 1) 1.0 A
UC1854A/BUC2854A/BUC3854A/B
Note 1: Guaranteed by design, not 100% tested in production.Note 2: Gain constant (K) = IAC (Va 1.5V)
VRMS 2 IMO
ELECTRICALCHARACTERISTICS (cont.)
Unless otherwise stated, VCC=18V, RT=8.2k, CT=1.5nF, PKLMT=1V, VRMS=1.5V, IAC=100A,ISENSE=0V, CA Out=3.5V, VA Out=5V, VSENSE=3V, 55oC
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offset of the UC1854A/B guarantees that the PWM circuitwill not drive the MOSFET if the current command is zero(both Current amplifier inputs zero.).Previous designsrequired an external offset cancellation network toimplement this key feature. The bandwidth of the CurrentAmplifier has been improved as well to 5mHz typical.While this is not generally an issue at 50 or 60Hz inputs, itis essential for 400Hz input avionics applications.MISCELLANEOUSSeveral other important enhancements have beenimplemented in the UC1854A/B. A VCC supply voltageclamp at 20V allows the controller to be current fed if
desired. The lower startup supply current (250A typical),substantially reduces the power requirements of an offlinestartup resistor. The 10.5/10V UVLO option (UC1854B)enables the controller to be powered off of an auxiliary12V supply.The VREF "GOOD" comparator guarantees that theMOSFET driver output remains low if the supply or the7.5V reference are not yet up. This improvementeliminates the need for external Schottky diodes on thePKL and CA+ pins that some UC1854 designs require.The propagation delay of the disable feature has beenimproved to 300ns typical. This delay was proportional to
FUNCTIONAL DESCRIPTION (cont.)
UC1854A/BUC2854A/BUC3854A/B
TYPICAL CHARACTERISTICS at TA = TJ = 25C
Load Capacitance, F
ns
0
100
200
300
400
500
600
700
0 0.01 0.02 0.03 0.04 0.05
Rise TimeFall Time
Gate Drive Rise and Fall Time
RSET, k
DutyCycle
70%
75%
80%
85%
90%
95%
100%
1 10 100
Gate Drive Maximum Duty Cycle
0 50 100 150 200 2500.8
0.840.880.920.96
11.041.081.121.161.2
K
IAC Current (A)
VRMS=1.5V
VRMS=3.0V
VRMS=5.0V
UC1854A/B Multiplier LinearityVAOUT = 3.5V
0 50 100 150 200 2500.8
0.840.880.920.96
11.041.081.121.161.2
K
IAC Current (A)
VRMS=3.0VVRMS=
1.5V
VRMS=5.0V
UC1854A/B Multiplier LinearityVAOUT = 5V
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TYPICAL CHARACTERISTICS at TA = TJ = 25C (cont.)
UNITRODE CORPORATION7 CONTINENTAL BLVD. MERRIMACK, NH 03054TEL. (603) 424-2410 FAX (603) 424-3460 These products contain patented circuitry and are sold under license from Pioneer Magnetics, Inc.
UC1854A/BUC2854A/BUC3854A/B
log f
Gai
n (dB
)
-60
-40
-20
0
20
40
60 0
80 -45 PhaseDegrees
100 -90
120
10kHz 1MHz 10MHz100kHz
Gain
Phase
5.992 496 516 MHz
Current Amplifier Frequency Response
RSET, k
FrequencykHz
10
100
1000
1 10 100
100pF
200pF
5nF10nF 3nF
500pF
2nF
1nF
Oscillator Frequency vs RSET and CT
FrequencykHz
PhaseMargindegrees
Open-LoopGaindB
-20
0
20
40
60
80
100
120
0.1 1 10 100 1000 10000
Voltage Amplifier Gain and Phase vs Frequency
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Copyright 1999, Texas Instruments Incorporated
Design Notes
