LT3504: Quad 1A Buck Regulator with 180V Surge Protection

The LT3504 is a 4-channel monolithic step-down regulator designed for 100% duty cycle operation. Its unique architecture makes available a bias voltage, which is easily adapted to an N-channel protection scheme, allowing the LT3504 to operate continuously through overvoltage transients and dropouts down to 3.2V. Among its many features, the LT3504 includes output voltage tracking and sequencing, programmable frequency, programmable undervoltage lockout, and a power good pin to indicate when all outputs are in regulation.

The firgure shown is a complete application circuit for a 4-output, 1A step-down regulator operating over a 3.2V to 30V range. Q1 provides surge protection to 180V. An on-chip boost regulator generates a voltage rail (VSKY) that is 5V greater than the input voltage VIN. Under normal operating conditions (VIN < 33V), the VSKY rail supplies gate drive to MOSFET Q1, providing the LT3504 with a low resistance path to VSUPPLY. Additionally, the VSKY pin supplies base drive for the switches in each buck converter channel, which allows for 100% duty cycle and eliminates the need for the boost capacitor typically found in buck converters.

 

Software

LTspice