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UC3842T 数据表(PDF) 1 Page - STMicroelectronics |
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UC3842T 数据表(HTML) 1 Page - STMicroelectronics |
1 / 15 page UC3842T UC3843T UC3844T UC3845T September 2001 HIGH PERFORMANCE CURRENT MODE PWM CONTROLLER . 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 DESCRIPTION The UC384XT 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. Internally imple- mented circuits include a trimmed oscillator for pre- cise DUTY CYCLE CONTROL under voltage lock- out featuring start-up current less than 0.5mA, a pre- cision reference trimmed for accuracy at the error amp input, logic to insure latched operation, a PWM comparator 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 UC3842T and UC3844T have UVLO thresholds of 16V (on) and 10V (off), ideally suited to off-line applications The corresponding thresholds for the UC3843T and UC3845T are 8.5 V and 7.9 V. The UC3842T and UC3843T can operate to duty cycles approaching 100%. A range of zero to < 50 % is obtained by the UC3844T and UC3845T by the addition of an internal toggle flip flop which blanks the output off every other clock cycle. BLOCK DIAGRAM (toggle flip flop used only in UC3844T and UC3845T) UVLO S/R 5V REF 34V INTERNAL BIAS VREF GOOD LOGIC 2.50V T S R OSC R1V CURRENT SENSE COMPARATOR 2R + - PWM LATCH 7 5 4 2 1 3 8 6 ERROR AMP. Vi GROUND RT/CT VFB COMP CURRENT SENSE VREF 5V 50mA OUTPUT D95IN331 Minidip ® SO8 1/15 |
类似零件编号 - UC3842T |
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类似说明 - UC3842T |
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