Adaptive On-Time Converters

摘要

Pulse frequency modulation (PFM) converters are fast in response and simple in design and implementation because compensation is not required. However, the large variation of switching frequency during operation introduces electromagnetic interference (EMI) problems. This article proposes a mixed analog and digital adaptive on-time (AOT) controller for PFM converters so that the switching frequency can be maintained constant adaptively, while the transient response is not degraded. The transient response is handled by an analog controller, which is fast. The switching frequency regulation is implemented by a digital microcontroller. Since the digital control loop is a slow outer control loop, low-cost digital circuits can be used. However, high-performance converters can be obtained by embedding analog and digital control. Hardware results will show that the proposed mixed analog and digital control can successfully implement a fast transient-response converter with a substantially constant switching frequency.