UC2842B STMicroelectronics, UC2842B Datasheet

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UC2842B

Manufacturer Part Number
UC2842B
Description
HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER UC2842BHIGH PERFORMANCE CURRENT MODE PWM CONTROLLER
Manufacturer
STMicroelectronics
Datasheet

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TheUC384xB family ofcontrolICs providesthe nec-
essary features to implement off-line or DC to DC
fixed frequency current mode control schemes with
a minimal external parts count. Internally imple-
mented circuits include a trimmed oscillator for pre-
cise DUTY CYCLE CONTROL under voltage lock-
outfeaturingstart-up current less than0.5mA,a pre-
cision reference trimmed for accuracy at the error
amp input, logicto insure latched operation,a PWM
BLOCK DIAGRAM (toggle flip flop used only in UC3844B and UC3845B)
March 1999
HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER
DESCRIPTION
TRIMMED OSCILLATOR FOR PRECISE FRE-
QUENCY CONTROL
OSCILLATOR FREQUENCY GUARANTEED
AT 250kHz
CURRENT MODE OPERATION TO 500kHz
AUTOMATIC FEED FORWARD COMPENSA-
TION
LATCHING PWM FOR CYCLE-BY-CYCLE
CURRENT LIMITING
INTERNALLY TRIMMED REFERENCE WITH
UNDERVOLTAGE LOCKOUT
HIGH CURRENT TOTEM POLE OUTPUT
UNDERVOLTAGE LOCKOUT WITH HYSTER-
ESIS
LOW START-UP AND OPERATING CURRENT
CURRENT
GROUND
SENSE
RT/CT
COMP
VFB
Vi
7
5
4
2
1
3
34V
+
-
ERROR AMP.
OSC
2.50V
UVLO
2R
R
S/R
REF
5V
1V
VREF GOOD
LOGIC
comparatorwhich alsoprovidescurrent limit control,
and a totem pole output stage designed to source
or sink high peakcurrent. The outputstage, suitable
for driving N-Channel MOSFETs, is low in the off-
state.
Differences between members of this family are the
under-voltagelockout thresholds and maximum duty
cycle ranges. The UC3842B and UC3844B have
UVLO thresholds of 16V (on) and 10V (off), ideally
suitedoff-lineapplicationsThecorrespondingthresh-
oldsforthe UC3843BandUC3845Bare8.5 V and7.9
V. The UC3842B and UC3843B can operate to duty
cycles approaching 100%. A range of the zero to <
50 % is obtained by the UC3844B and UC3845B by
the addition of an internal toggle flip flopwhich blanks
the output off every otherclock cycle.
COMPARATOR
CURRENT
SENSE
UC2842B/3B/4B/5B
UC3842B/3B/4B/5B
S
R
INTERNAL
T
BIAS
Minidip
LATCH
PWM
UC3842B
D95IN331
8
6
5V 50mA
OUTPUT
SO8
VREF
1/15

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UC2842B Summary of contents

Page 1

... VFB - 1 COMP 3 CURRENT SENSE March 1999 UC2842B/3B/4B/5B UC3842B/3B/4B/5B Minidip comparatorwhich alsoprovidescurrent limit control, and a totem pole output stage designed to source or sink high peakcurrent. The outputstage, suitable for driving N-Channel MOSFETs, is low in the off- state. Differences between members of this family are the under-voltagelockout thresholds and maximum duty cycle ranges ...

Page 2

... UC2842B/3B/4B/5B - UC3842B/3B/4B/5B ABSOLUTE MAXIMUM RATINGS Symbol V Supply Voltage (low impedance source Supply Voltage (Ii < 30mA Output Current O E Output Energy (capacitive load) O Analog Inputs (pins 2, 3) Error Amplifier Output Sink Current P Power Dissipation at T tot amb P Power Dissipation at Tamb ...

Page 3

... OUT CURRENT SENSE SECTION G Gain V V Maximum Input Signal 3 SVR Supply Voltage Rejection I Input Bias Current b Delay to Output UC2842B/3B/4B/5B - UC3842B/3B/4B/5B Minid ip max. 100 < for UC384XB 15V (note 5); R amb i UC284XB T est Cond it ion s Min. Typ. Max. Min. Typ. Max. 4.95 5.00 5.05 4.90 5.00 5. ...

Page 4

... UC2842B/3B/4B/5B - UC3842B/3B/4B/5B ELECTRICAL CHARACTERISTICS (continued) Symbo l Parameter OUTPUT SECTION V Output Low Level OL V Output High Level OH V UVLO Saturation OLS t Rise Time r t Fall Time f UNDER-VOLTAGE LOCKOUT SECTION Start Threshold Min Operating Voltage After Turn-on PWM SECTION Maximum Duty Cycle Minimum Duty Cycle ...

Page 5

... =5nF =2nF T C =10nF =15V 0.8 10K 20K 30K 50K 100K 200K 300K UC2842B/3B/4B/5B - UC3842B/3B/4B/ REF 0.1 F COMP 0.1 F UC2842B I SENSE 3 OUTPUT GROUND pin single point ground. The transistor and 5 K potentiometerareusedto samplethe oscillator waveform and apply an adjustable ramp to pin 3 ...

Page 6

... UC2842B/3B/4B/5B - UC3842B/3B/4B/5B Figure 4: Oscillator Discharge Current vs. Tem- perature. I dischg (mA) V =15V i V =2V OSC 8.5 8.0 7.5 7.0 -55 - Figure 6: Error Amp Open-Loop Gain and Phase vs. Frequency. (dB) V =15V =100K L Gain T = -20 10 100 1K 10K 100K 1M Figure 8: Reference Voltage Change vs. ...

Page 7

... Figure 12: Output Waveform. 90% 10% 50ns/DIV Figure 14: Oscillator and Output Waveforms REG PWM R T CLOCK 4 OSCILLATOR UC2842B/3B/4B/5B - UC3842B/3B/4B/5B Figure 11: Supply Current vs. Supply Voltage D95IN341 (mA GND (mA) O Figure 13: Output Cross Conduction V =15V ...

Page 8

... UC2842B/3B/4B/5B - UC3842B/3B/4B/5B Figure 15 : Error Amp Configuration Figure 16 : Under Voltage Lockout. 7 ON/OFF COMMAND V TO REST UC3842B UC3844B V 16V ON V 10V OFF Figure 17 : Current Sense Circuit . I S COMP R CURRENT SENSE GND D95IN347 Peak current ( determined by the formula s 1 max ...

Page 9

... UC3842B R C SLOPE SENSE Figure 19 : Isolated MOSFET Drive and Current Transformer Sensing 5.0V ref - + - COMP/LATCH D95IN349 UC2842B/3B/4B/5B - UC3842B/3B/4B/ SLOPE GND V ISOLATION BOUNDARY REG UC3842B ...

Page 10

... UC2842B/3B/4B/5B - UC3842B/3B/4B/5B Figure 20 : Latched Shutdown. 2N 3905 SCR must be selected for a holding current of less than 0.5mA at T The simple two transistor circuit can be used in place of the SCR as shown. All resistors are 10K. Figure 21: Error Amplifier Compensation From Error Amp compensation circuit for stabilizing any current-mode topology except for boost and flyback converters operating with continuous inductor current ...

Page 11

... Figure 23: External Duty Cycle Clamp and Multi Unit Synchronization. V REF NE555 1 1. max ( UC2842B/3B/4B/5B - UC3842B/3B/4B/5B V REF BIAS OSC D95IN352 R BIAS R OSC + 2R + ...

Page 12

... UC2842B/3B/4B/5B - UC3842B/3B/4B/5B Figure 24: Soft-Start Circuit Figure 25: Soft-Start and Error Amplifier Output Duty Cycle Clamp 1mA + BC109 · CLAMP 12/15 5V ref R BIAS R OSC + 1mA ref + BIAS - OSC V S Clamp Comp/Latch ...

Page 13

... F (1) 3.8 4.0 0.15 L 0.4 1.27 0.016 M 0 (max.) (1) D and F do not include mold flash or protrusions. Mold flash or potrusions shall not exceed 0.15mm (.006inch). UC2842B/3B/4B/5B - UC3842B/3B/4B/5B inch OUTLINE AND TYP. MAX. MECHANICAL DATA 0.069 0.010 0.065 0.033 0.019 0.010 0.020 0.197 0.244 0.050 0.150 ...

Page 14

... UC2842B/3B/4B/5B - UC3842B/3B/4B/5B mm DIM. MIN. TYP. MAX. MIN. A 3.32 a1 0.51 0.020 B 1.15 1.65 0.045 b 0.356 0.55 0.014 b1 0.204 0.304 0.008 D 10.92 E 7.95 9.75 0.313 e 2.54 e3 7.62 e4 7.62 F 6.6 I 5.08 L 3.18 3.81 0.125 Z 1.52 14/15 inch OUTLINE AND MECHANICAL DATA TYP. MAX. 0.131 0.065 0.022 0.012 0.430 0.384 0.100 0.300 0.300 0.260 0.200 0.150 0.060 ...

Page 15

... The ST logo is a registered trademark of STMicroelectronics 1999 STMicroelectronics – Printed in Italy – All Rights Reserved STMicroelectronics GROUP OF COMPANIES Australia - Brazil - Canada - China - France - Germany - Italy - Japan - Korea - Malaysia - Malta - Mexico - Morocco - The Netherlands - Singapore - Spain - Sweden - Switzerland - Taiwan - Thailand - United Kingdom - U.S.A. UC2842B/3B/4B/5B - UC3842B/3B/4B/5B http://www.st.com 15/15 ...

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