YL. SGS-THOMSON MICROELECTROMICS UC2842/3/4/5 UC3842/3/4/5 CURRENT MODE PWM CONTROLLER ' For complete specification refer to" Linear & Switching Voltage Regulators Appi. Manual . (Order Code AMLISVOREST/1 ) s OPTIMIZED FOR OFF-LINE AND DC TO DC , CONVERTERS | a LOW START-UP CURRENT (< 1 mA) | @ AUTOMATIC FEED FORWARD COMPENSA- ' TION , : m PULSE-BY-PULSE CURRENT LIMITING / ENHANCED LOAD RESPONSE CHARAC- : TERISTICS : a UNDER-VOLTAGE LOCKOUT WITH HYS- : TERESIS DOUBLE PULSE SUPPRESSION HIGH CURRENT TOTEM POLE OUTPUT a INTERNALLY TRIMMED BANDGAP REFER- ENCE # 500 KHz OPERATION | p LOW Ro ERROR AMP . DESCRIPTION : The UC3842/3/4/5 family of control ICs provides the necessary features to implement off-line or DC to _ DC fixed frequency current mode control schemes with a minimal external parts count. tntemally im- plemented circuits include under voltage lockout featuring start-up current less than 1 mA, aprecision reference trimmed for accuracy at the error amp Minidip input, logic to insure latched operation, a PWM com- parator which also provides current limit control, and a totem pole output stage designed to source or sink high peak current. The output stage, suitable for driving N-Channel MOSFETs, is low in the off-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 thre- sholds for the UC3843 and UC3845 are 8.5 V and 7.9V. 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 addition of an interna! toggle flip flop which blanks the output off every other clock cycle. BLOCK DIAGRAM (toggle flip flop used only in U3844 and UC3845) ui ' au UULO a/R 5Y (14981 uRer GROUND ll REF 5U 5emA "| INTERNAL 2.5eu | BIAS au7t oy UREF GOOD Losrc : LL 5 OUTPUT |} RT/CT 4c?) osc. ouTPU : ERROR ANP, ) POVER p GROUND PUM | Fe et atcn comp CURRENT SENSE CURRENT COMPARATOR UC3842 SENSE NI2ZUE3I042-82 October 1991 1/8 819