PWM controller for buck and push-pull converters
The STMicroelectronics SG3525AP013TR is a PWM controller IC designed for step-down (buck) and step-up/step-down (push-pull) topologies. It integrates a transistor driver output stage, clock synchronization capability, and control features including enable and soft start. The device operates from an 8V to 35V supply rail and supports a switching frequency range from 100Hz to 400kHz, with a maximum duty cycle of 49%.
49% duty cycle — why it matters for push-pull
The 49% maximum duty cycle is a deliberate design choice for push-pull converters. It leaves a dead-time gap that prevents simultaneous conduction of both primary-side switches, avoiding transformer saturation and shoot-through current. For buck designs, the same limit still provides adequate output voltage range at typical input-to-output ratios. If your design requires duty cycles above 50%, this controller will not support it — you would need a different topology or a controller with a wider duty-cycle window.
Switching frequency range — sizing the magnetics
The 100Hz to 400kHz switching frequency range gives the designer room to trade off magnetics size against switching losses. At the lower end, transformer and inductor cores are larger but core losses are minimal — useful for noise-sensitive or high-efficiency designs. At the upper end, magnetics shrink but gate-drive and core losses increase. The clock sync feature allows multiple SG3525AP013TR controllers to run at the same frequency, which simplifies input filter design in multi-phase or paralleled converter systems.
The base product number is SG3525, which shares the same pinout and function across the family — if you already use a through-hole or DIP variant, the SOIC-16 footprint is the only difference.
The SG3525AP013TR is supplied in a 16-pin SOIC package with a 3.90mm body width, surface-mount only. The supplier device package is designated 16-SO. No through-hole variant is available for this order code.