UC3844A

LIN D O C # : 1840 UC184xA/284xA/384xA CURRENT MODE PWM CONTROLLER T HE I NFINITE P OWER OF I N N O VAT I O N P RODUCTION D ATA S HEET DESCRIPTION The UC184xA family of control ICs provides all the necessary features to implement off-line fixed-frequency, current-mode switching power supplies with a minimum of external components. The current mode architecture demonstrates improved load regulation, pulse-by-pulse current limiting and inherent protection of the power supply output switch. The IC includes: A bandgap reference trimmed to ±1% accuracy, an error amplifier, a current sense comparator with internal clamp to 1V, a high current totem pole output stage for fast switching of power MOSFET's, and an externally programmable oscillator to set frequency and maximum duty cycle. The undervoltage lock-out is designed to operate with 250µA typ. start-up current, allowing an efficient bootstrap supply voltage design. Available options for this family of products, such as start-up voltage hysteresis and duty cycle, are summarized below in the Available Options section. The UC184xA family of control ICs is also available in 14-pin SOIC package which makes the Power Output Stage Collector and Ground pins available. K E Y F E AT U R E S s LOW START-UP CURRENT. (0.5mA max.) s TRIMMED OSCILLATOR DISCHARGE CURRENT. (See Product Highlight) p OPTIMIZED FOR OFF-LINE AND DC-TO-DC CONVERTERS. p AUTOMATIC FEED FORWARD COMPENSATION. p PULSE-BY-PULSE CURRENT LIMITING. p ENHANCED LOAD RESPONSE CHARACTERISTICS. p UNDER-VOLTAGE LOCKOUT WITH HYSTERESIS. p DOUBLE PULSE SUPPRESSION. p HIGH-CURRENT TOTEM POLE OUTPUT. p INTERNALLY TRIMMED BANDGAP REFERENCE. p 500KHz OPERATION. p LOW RO ERROR AMPLIFIER. PRODUCT HIGHLIGHT COMPARISON OF U C384 X A VS. SG384 X D ISCHARGE C URRENT A P P L I C AT I O N S SG384x Max. Limit UC384xA SG384x Min. Limit TA=25°C s ECONOMICAL OFF-LINE FLYBACK OR FORWARD CONVERTERS. s DC-DC BUCK OR BOOST CONVERTERS. s LOW COST DC MOTOR CONTROL. A VAILABLE O PTIONS Part # UCx842A UCx843A 7.5 7.8 8.3 Mean 8.8 9.3 Start-Up Hysteresis Max. Duty Voltage Cycle 16V 8.4V 16V 8.4V 6V 0.8V 6V 0.8V