Overview
The IS32LT3957 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 IS32LT3957 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 IS32LT3957
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 IS32LT3957 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.