UC2843 STMicroelectronics, UC2843 Datasheet

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UC2843

Manufacturer Part Number
UC2843
Description
Manufacturer
STMicroelectronics
Datasheet

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DESCRIPTION
TheUC3842/3/4/5family of controlICs provides the
necessary features to implement off-line or DC to
DC fixed frequency current mode control schemes
with a minimal externalparts count.Internallyimple-
mentedcircuits include undervoltagelockout featur-
ing start-up current less than 1 mA, a precision ref-
erence trimmed for accuracy at the error amp input,
BLOCK DIAGRAM (toggle flip flop used only in U3844 and UC3845)
October 1998
OPTIMIZED FOR OFF-LINE AND DC TO DC
CONVERTERS
LOW START-UP CURRENT (< 1 mA)
AUTOMATIC FEED FORWARD COMPENSA-
TION
PULSE-BY-PULSE CURRENT LIMITING
ENHANCED LOAD RESPONSE CHARAC-
TERISTICS
UNDER-VOLTAGE LOCKOUT WITH HYSTER-
ESIS
DOUBLE PULSE SUPPRESSION
HIGH CURRENT TOTEM POLE OUTPUT
INTERNALLY TRIMMED BANDGAP REFER-
ENCE
500 KHz OPERATION
LOW R
O
ERROR AMP
CURRENT MODE PWM CONTROLLER
logic to insure latched operation, a PWM compara-
torwhich also providescurrentlimit control,and a to-
tem pole output stage designed to source or sink
high peak current. The output stage, suitable for
driving N-Channel MOSFETs, is low in theoff-state.
Differences between members of this family are the
under-voltage lockout thresholds and maximum
duty cycle ranges. The UC3842 and UC3844 have
UVLO thresholds of 16V (on) and 10V (off), ideally
suited off-line applications The corresponding
thresholds for the UC3843 and UC3845 are 8.5 V
and 7.9 V. The UC3842 and UC3843 can operate
to duty cycles approaching 100%. A range of the
zero to < 50 % is obtained by the UC3844 and
UC3845 by the additionof an internal toggle flip flop
which blanks the output off every other clock cycle.
Minidip
UC2842/3/4/5
UC3842/3/4/5
SO14
1/11

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UC2843 Summary of contents

Page 1

OPTIMIZED FOR OFF-LINE AND CONVERTERS . LOW START-UP CURRENT (< 1 mA) AUTOMATIC FEED FORWARD COMPENSA- . TION . PULSE-BY-PULSE CURRENT LIMITING ENHANCED LOAD RESPONSE CHARAC- . TERISTICS UNDER-VOLTAGE LOCKOUT WITH HYSTER- . ESIS . ...

Page 2

... UC2842N UC2843N UC2844N UC2845N UC3842N UC3843N UC3844N UC3845N Min id ip max. Value Unit 30 V Self Limiting – 0 725 mW – 150 C 300 C Minidip SO14 UC2842D UC2843D UC2844D UC2845D UC3842D UC3843D UC3844D UC3845D SO14 Unit 100 165 C ...

Page 3

ELECTRICAL CHARACTERISTICS (Unless otherwise stated, these specifications apply for -25 < for UC2824X; 0 < T < for UC384X; V amb Symbo l Parameter V Output Voltage REF Line Regulation V REF Load Regulation V ...

Page 4

UC2842/3/4/5-UC3842/3/4/5 ELECTRICAL CHARACTERISTICS (continued) Symbo l Parameter UNDER-VOLTAGE LOCKOUT SECTION Start Threshold Min Operating Voltage After Turn-on Maximum Duty Cycle Minimum Duty Cycle I Start-up Current st I Operating Supply Current i V Zener Voltage iz N otes : 2. ...

Page 5

Figure 1 : Error Amp Configuration. Error amp can source or sink up to 0.5mA Figure 2 : Under Voltage Lockout. During Under-Voltage Lockout, the output driver is biased to sink minor amounts of current. Pin 6 should be shunted ...

Page 6

UC2842/3/4/5-UC3842/3/4/5 Figure 4. 1.72 for R > Figure 6 : Timing Resistance vs. Frequency. Figure 8 : Error Amplifier Open-loop Frequency Response. 6/11 Figure 5 : Deadtime vs > 5K ...

Page 7

Figure 9 : Open Loop Test Circuit. High peak currents associatedwith capacitive loads necessitate careful grounding techniques. Timing and bypass capacitors should be connected close Figure 10 : Shutdown Techniques. Shutdown of the UC2842 can be accomplished by two methods; ...

Page 8

UC2842/3/4/5-UC3842/3/4/5 Figure 11 : Off-line Flyback Regulator. Power Supply Specifications 1. Input Voltage : 95 VAC to 130 VAC (50 Hz/60 Hz) 2. Line Isolation : 3750 V 3. Switching Frequency : 40 KHz 4. Efficiency @ Full Load : ...

Page 9

DIM. MIN.. TYP. MAX.. MIN.. A 1.75 a1 0.1 0.25 0.004 a2 1.6 b 0.35 0.46 0.014 b1 0.19 0.25 0.007 C 0 (typ.) D (1) 8.55 8.75 0.336 E 5.8 6.2 0.228 e 1.27 e3 7.62 ...

Page 10

UC2842/3/4/5-UC3842/3/4/5 mm DIM. MIN. TYP. MAX. MIN. A 3.3 a1 0.7 0.028 B 1.39 1.65 0.055 B1 0.91 1.04 0.036 b 0.5 b1 0.38 0.5 0.015 D 9.8 E 8.8 e 2.54 e3 7.62 e4 7.62 F 7.1 I 4.8 ...

Page 11

... No license is granted by implication or otherwise under any patent or patent rights of STMicroelectronics. Specification mentioned in this publication are subject to change without notice. This publication supersedes and replaces all information previously supplied. STMi- croelectronics products are not authorized for use as critical components in life support devices or systems without express written approval of STMicroelectronics ...

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