A Wide Input Voltage Range Buck Converter with Constant-Charge PFM Control

Pulse frequency modulation (PFM) is widely used in buck converters to improve the efficiency at light loads. An adaptive on-time (AOT) control is usually adopted in wide input voltage range converters to mitigate the strong output voltage ripple variation. This paper presents a 6-V to 32-V input voltage, PFM buck converter with a novel AOT control that provides constant-charge current pulses over the whole input voltage range, resulting in an almost constant output voltage ripple. The prototype buck converter is fabricated in a 180-nm BCD process, and it provides an output voltage of 3.3-V and maximum load current of 100-mA with 92% peak efficiency. The proposed AOT control, which occupies only 0.04-mm(2), keeps the output voltage ripple almost constant around 40-mV, with a variation of only 7.5-mV over the whole input range.