ISSI IS31LT3957A

Description

The IS31LT3957A is a current mode PWM controller designed to drive a low side external NMOS FET for wide input/output voltage range and high LED current applications. An external resistor senses the high side output current of the LED string. A high side sense is the most flexible current sensing scheme, since it functions in either boost or buck-boost mode configurations. The controller can be configured with an external resistor to operate between 100kHz~1MHz frequency resulting in small external inductor and capacitors while maintaining high efficiency. A single capacitor is all that is required to set the spread spectrum dither frequency to reduce the radiated peak emission and optimize the system EMI performance. The IS31LT3957A integrates circuity to detect output open/short, RT/SYNC pin short, VDD short, VCC under voltage lockout and over temperature fault conditions. These failure conditions can be reported by the open drain fault reporting FAULTB pin. An MCU can be easily interfaced with the IS31LT3957A to perform dimming control and respond to fault report conditions. Dimming can be either analog and/or PWM input. An input DC voltage in the range of 0.1V ~ 1.1V on the ICTRL pin is required for analog dimming. A digital signal with varying duty cycle on the PWM/EN pin will achieve PWM dimming. The IS31LT3957A is available in an eTSSOP-16 package with an exposed pad for enhanced thermal dissipation. It operates from 5V to 75V over the temperature range of -40°C to +125°C.

Features

• Wide high voltage input range: 5V to 75V
• Supports boost, buck-boost, SEPIC and buck topology
• ±3.5% output current accuracy over -40°C ~ +125°C temperature
• Adjustable operating frequency range of 100kHz~1MHz
• Programmable soft start to avoid inrush current
• Fixed under voltage lockout threshold
• EMI reduction capabilities
  • Programmable spread spectrum function
  • Operating frequency synchronization with external clock source
• Supports either analog or PWM dimming
• Fault protection with reporting:
  • VCC under voltage lockout (not reported)
  • Programmable output over voltage protection
  • Output short circuit protection
  • RT/SYNC pin short protection
  • VDD pin short protection
  • VDD under voltage lockout (not reported)
  • Over temperature protection
• AEC-Q100 Qualified (IS32LT3957A only)

Typical applications

• General high power LED , Architecture lighting, Motorcycle headlight, Exit Signs and Emergency Lighting

More information

• Datasheet
• IC product information