DESCRIPTION
Differences between members of this family are the under-voltagelockout thresholds and maximum duty TheUC384xB family ofcontrolICs providesthe nec- cycle ranges. Internally imple- oldsforthe UC3843BandUC3845Bare8.5 V and7.9 mented circuits include a trimmed oscillator for pre- V. A range of the zero to < outfeaturingstart-up current less than0.5mA,a pre- 50 % is obtained by the UC3844B and UC3845B by cision reference trimmed for accuracy at the error the addition of an internal toggle flip flopwhich blanks amp input, logicto insure latched operation,a PWM the output off every otherclock cycle. BLOCK DIAGRAM (toggle flip flop used only in UC3844B and UC3845B) 7 Vi 5 GROUND 4 RT/CT 2 VFB 1 COMP CURRENT 3 SENSE 34V UVLO S/R 5V REF 2.50V OSC VREF GOOD LOGIC INTERNAL BIAS T 8 VREF 5V 50mA 6 OUTPUT ERROR AMP. + 2R R S R 1V CURRENT SENSE COMPARATOR PWM LATCH UC3842B D95IN331 March 1999 1/15 UC2842B/3B/4B/5B - UC3842B/3B/4B/5B ABSOLUTE MAXIMUM RATINGS
Sy mb o l P ar ame te r Vi Sup...
STMicroelectronics
