View r1223n-series datasheet:

‘99.12.8 PWM/VFM step-down DC/DC Converter R1223N Series OUTLINE The R1223N Series are PWM step-down DC/DC Converter controllers with low supply current by CMOS process. Each of these ICs consists of an oscillator, a PWM control circuit, a reference voltage unit, an error amplifier, a soft-start circuit, a protection circuit, a PWM/VFM alternative circuit, a chip enable circuit, and resistors for voltage detection. A low ripple, high efficiency step-down DC/DC converter can be easily composed of this IC with only four external components, or a power-transistor, an inductor, a diode and a capacitor. With a PWM/VFM alternative circuit, when the load current is small, the operation is automatically switching into the VFM oscillator from PWM oscillator, therefore the e