5.3 Pulse Frequency Mode of Operation (PFM)

The MCP16367 selects the best operating switching mode (PFM or PWM) for high efficiency across a wide range of load currents. In PFM, the duty cycle is determined by a fixed peak current, which may cause the output voltage to rise slightly above the typical regulation point. When the output voltage increases and the feedback voltage exceeds 810 mV typical, the MCP16367 stops switching and enters Sleep mode. Normal operations resume when the output voltage decreases. By switching to PFM mode at light load currents and leveraging the device’s very low quiescent current (I_Q) when not switching, the MCP16367 achieves exceptionally high efficiency at very low loads. During the sleep period between switching bursts, the device draws only 18 μA (typical) from the supply. Since the switching pulse packets occupy a small portion of the total operating cycle, the average current drawn from the power supply remains minimal.

It is important to note that PFM/PWM operation can result in higher output voltage ripple and a variable PFM mode frequency. The threshold for entering PFM mode depends on the input voltage, output voltage, and load conditions.