Datasheet

UC2842/3/4/5
UC3842/3/4/5
May 1995
CURRENT MODE PWM CONTROLLER
.OPTIMIZED FOR OFF-LINE AND DC TO DC
CONVERTERS
.LOW START-UP CURRENT (< 1 mA)
.AUTOMATIC FEED FORWARD COMPENSA-
TION
.PULSE-BY-PULSECURRENT 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
DESCRIPTION
The UC3842/3/4/5family ofcontrolICsprovides the
necessary features to implement off-line or DC to
DC fixed frequency current mode control schemes
with aminimal externalpartscount.Internallyimple-
mentedcircuitsincludeundervoltagelockoutfeatur-
ing start-up current less than 1 mA, a precision ref-
erencetrimmed for accuracyat theerror ampinput,
logic to insure latched operation, a PWM compara-
torwhich alsoprovidescurrentlimit control,anda to-
tem pole output stage designed to source or sink
high peak current. The output stage, suitable for
driving N-ChannelMOSFETs, islow in the off-state.
Differencesbetween members of this family are the
under-voltage lockout thresholds and maximum
duty cycle ranges.The UC3842 and UC3844 have
UVLO thresholdsof 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 internaltoggleflip flop
which blanks the output off every other clock cycle.
BLOCK DIAGRAM (toggle flip flop used only in U3844 and UC3845)
Minidip
SO14
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