100kHz buck controller with 92% duty cycle ceiling
The Texas Instruments UC2573D is a current-mode PWM controller for step-down (buck) topologies, switching at 100kHz with a maximum duty cycle of 92%. The 4.75V to 30V supply range covers common 5V, 12V, and 24V intermediate buses without an external bias rail. The single transistor-driver output drives an external N-channel MOSFET or bipolar switch; synchronous rectification is not implemented internally, so the freewheeling diode sits outside the controller. The 92% duty ceiling means the output can approach the input voltage within about 8% headroom — useful for pre-regulator stages where dropout margin is tight.
Supply range, temperature grade, and control features
Control features include current-limit sensing and a ramp compensation pin — the ramp stabilises the current loop at duty cycles above 50%, preventing subharmonic oscillation in continuous-conduction mode. There is no clock synchronisation input, so the switching frequency is fixed by the internal oscillator at 100kHz.