IS31LT3957 HIGH VOLTAGE LED LIGHTING CONTROLLER WITH FAULT PROTECTION December 2018 GENERAL DESCRIPTION FEATURES The IS31LT3957 is a current mode PWM controller Wide high voltage input range: 5V to 75V designed to drive a low side external NMOS FET for Supports boost, buck-boost, SEPIC and buck wide input/output voltage range and high LED current topology applications. An external resistor senses the high side 2% output current accuracy output current of the LED string. A high side sense is Adjustable operating frequency range of the most flexible current sensing scheme, since it 100kHz~1MHz functions in either boost or buck-boost mode Programmable soft start to avoid inrush current configurations. The controller can be configured with an external resistor to operate between 100kHz~1MHz Fixed under voltage lockout threshold frequency resulting in small external inductor and EMI reduction capabilities capacitors while maintaining high efficiency. A single - Programmable spread spectrum function capacitor is all that is required to set the spread - Operating frequency synchronization with spectrum dither frequency to reduce the radiated peak external clock source emission and optimize the system EMI performance. Supports either analog or PWM dimming The IS31LT3957 integrates circuity to detect output Fault protection with reporting: open/short, RT/SYNC pin short, VDD short, VCC - VCC under voltage lockout (not reported) under voltage lockout and over temperature fault - Programmable output over voltage protection conditions. These failure conditions can be reported by the open drain fault reporting FAULTB pin. - Output short circuit protection - RT/SYNC pin short protection An MCU can be easily interfaced with the IS31LT3957 - VDD pin short protection to perform dimming control and respond to fault report - VDD under voltage lockout (not reported) conditions. Dimming can be either analog and/or PWM input. An input DC voltage in the range of 0.1V ~ 1.1V - Over temperature protection on the ICTRL pin is required for analog dimming. A APPLICATIONS digital signal with varying duty cycle on the PWM/EN pin will achieve PWM dimming. General high power LED Architecture lighting The IS31LT3957 is available in an eTSSOP-16 Motorcycle headlight package with an exposed pad for enhanced thermal Exit Signs and Emergency Lighting dissipation. It operates from 5V to 75V over the temperature range of -40C to +125C. Lumissil Microsystems www.lumissil.com 1 Rev. A, 12/20/2018 IS31LT3957 TYPICAL APPLICATION CIRCUIT V CC D 1 L 1 V OUT C OUT C IN 1 15 R O1 VCC GATE M 1 C VCC 13 CS 4.7 F 3 R O2 FAULTB R CS Optional 2 9 PWM/EN OVP 11 RPWM CPWM PWM ISP 1k 30pF R IS IS31LT3957 6 COMP 10 16 ISN VDD RDIM 14 100 LED C C 8 CP VDD DIMOUT String R ICTRL ICTRL 220nF 1 F *Note 1 CSS 4 5 FRQSS R NTC SGND 12 7 RRT M 2 PGND RT/SYNC Figure 1 Typical Application Circuit (Boost Configuration) Figure 2 Typical Application Circuit (Buck-Boost Configuration) Lumissil Microsystems www.lumissil.com 2 Rev. A, 12/20/2018