PWM controller for push-pull and buck — the 49% duty cycle ceiling
The onsemi SG3525AN is a PWM controller designed for step-down, step-up/step-down, buck, and push-pull topologies. Its defining parametric limit is a 49% maximum duty cycle per output — a deliberate constraint that prevents flux walking in push-pull and half-bridge transformers by guaranteeing a dead-time gap between the two output phases. The switching frequency spans 100 Hz to 400 kHz, with a built-in clock sync pin for synchronizing multiple converters or locking to an external system clock. The controller includes soft-start and enable control features, and supports synchronous rectification.
Obsolete — sourcing via independent distribution
Soft start and enable — sequencing without external glue
The integrated soft start ramps the duty cycle from zero on power-up, limiting inrush current and preventing output overshoot. The enable pin allows the controller to be gated by a supervisor or power-good signal, simplifying power-rail sequencing in multi-rail systems.