Dimmable Buck LED Driver - AC Mains or DC Input LED Driver ISL1903 Features The ISL1903 is a high-performance, critical conduction mode Excellent LED current regulation over line, load, and (CrCM), single-ended buck LED driver controller. It may be used temperature with DC input converters, but also supports single-stage 0 - 100% dimming with leading-edge (triac) and conversion of the AC mains to a constant current source with trailing-edge dimmers power factor correction (PFC). The ISL1903 supports buck Power factor correction for up to 0.995 power factor and converter topologies, such as isolated forward converters or less than 20% harmonic content non-isolated source return buck converters. Operation in CrCM allows near zero-voltage switching (ZVS) for improved Critical conduction mode (CrCM) operation for efficiency while maximizing magnetic core utilization. quasi-resonant high efficiency performance Supports Universal AC Mains Input The ISL1903 is compatible with both leading and trailing edge modulated AC mains dimmers. It provides all of the features Configurable for PWM or DC current dimming control of required for high-performance dimmable LED ballast designs. LEDs Monitors FET switching current for load regulation Applications Supports isolated and non-isolated buck topologies Industrial and commercial LED lighting Closed loop soft-start for no overshoot Retrofit LED lamps with triac dimming OFFREF feature to set dimming off-point to improve fixture Universal AC mains input LED retrofit lamps performance matching AC or DC input LED ballasts -40C to +125C operation Pb-free (RoHS compliant) 100 90 80 1 5 70 VDD CS+ 60 14 12 DHC AC 50 OUT 16 ISL1903 40 8 EMI Filter DELADJ OC 6 30 13 GND VERR 9 20 3 VREF FB 7 10 RAMP IOUT 0 10 4 100 90 80 70 60 50 40 30 20 10 0 AC Mains CONDUCTION ANGLE (%) FIGURE 1A. BOOST-RETURN (BUCK) TOPOLOGY FIGURE 1B. CURRENT vs AC CONDUCTION ANGLE FIGURE 1. ISL1903 APPLICATION PERFORMANCE September 20, 2012 CAUTION: These devices are sensitive to electrostatic discharge follow proper IC Handling Procedures. 1 1-888-INTERSIL or 1-888-468-3774 Copyright Intersil Americas Inc. 2012. All Rights Reserved FN8285.1 Intersil (and design) is a trademark owned by Intersil Corporation or one of its subsidiaries. All other trademarks mentioned are the property of their respective owners. Dimmer LED CURRENT (%)ISL1903 FN8285.1 2 September 20, 2012 Functional Block Diagram - ISL1903 VREF BIAS AND VDD REFERENCE GENERATOR UVLO + - OTP BG SHUTDOWN 150C TO 170C GND BIAS/UVLO/OTP DHC DUTY CYCLE TO VOLTAGE CONVERTER LOW PASS FILTER REFERENCE OUT DIMMING PWM TRIANGLE WAVE GENERATOR CLK MASTER CLK - OSCILLATOR PWMOUT + REF REFINBUFF PEAK DETECTOR AC-PRESENT AC DETECTION - AC + MINIMUM DIMMING LEVEL OUT CONTROL OFFREF + - PRIMARY CURRENT IOUT SENSE PROCESSOR INHIBIT INHIBIT CS+ + IOUT - REFERENCE SS + + ISENSE + OVP REFERENCE - 1.50V SS BUFFER DELADJ SS 300ms - QUASI-ZVS SOFT-START DELAY + ENABLE CRCM VERR CLAMP DETECTOR F F MAX MIN CLAMP CLAMP PWM - S Q LEADING + EDGE + OC BLANKING 600mV - R Q PRIMARY OC PWM LATCH SS LOW 0.25V + + RAMP - - 200mV - PWM VERR/5 SS/5 COMPARATOR SS 1/5 1/5 FAULT LATCH S Q REFINBUFF + EA1 - R Q VERR SOFT-START/POR/OVP CRCM OSCILLATOR/PWM/ERROR AMPLIFIERS VERR FB1