Demonstration circuit 949A is a 4.5A peak switch current boost LED driver with PWM dimming featuring the LT3478/LT3478-1. The LT3478 can be used for boost, buck mode, and buck-boost mode LED drivers. DC949A-A includes the LT3478-1, a fixed 1A boost LED driver with the LED current sense resistor inside the IC. DC949A-B features the LT3478 adjustable current boost LED driver; it requires an external sense resistor (R11). Both circuits are optimized to drive a 350mA LED string with a total LED voltage above the input voltage and below 40V (overvoltage protection is set between 36V and 40V).
The IC's input voltage range is 2.8V to 16V and the LED power input voltage range is 2.8V to 25V (for VLED > 25V). With an internal 4.5A NPN power switch, floating current sense amplifier, LED current PWM dimming control, inrush current protection, programmable switching frequency, soft-start, and overvoltage protection, the LT3478-1/LT3478 are extremely powerful and versatile LED driving ICs.