Hysteretic PFET Buck Controller with Enable Pin

The LM3489 device is a high-efficiency PFET switching regulator controller that can be used to quickly and easily develop a small, cost-effective, switching buck regulator for a wide range of applications. The hysteretic control architecture provides for simple design without any control loop stability concerns using a wide variety of external components. The PFET architecture also allows for low component count as well as ultra-low dropout, 100% duty cycle operation. Another benefit is high efficiency operation at light loads without an increase in output ripple. A dedicated enable pin provides a shutdown mode drawing only 7 µA. Leaving the enable pin unconnected defaults to on.

Current limit protection can be implemented by measuring the voltage across the PFET’s RDS(ON), thus eliminating the need for a sense resistor. A sense resistor may be used to improve current limit accuracy if desired. The cycle-by-cycle current limit can be adjusted with a single resistor, ensuring safe operation over a range of output currents.