Frequency compensation circuit for adaptive on-time control buck regulator

A novel frequency compensation circuit for adaptive on-time control buck regulator is presented in this study, which mainly applied to provide power supply for double data rate synchronous dynamic random access memory system. Typical ripple control regulator possesses the advantage of fast transient response and unconditional stability. However, it suffers significant steady-state switching frequency variation when the input voltage and output voltage are varied. The on-time is directly proportional to the output voltage and inversely proportional to the input voltage so that the regulator can dynamically adjust the turn-on time of power switches according to the changes of input voltage and output voltage in steady-state operation by adaptive on-time control. Finally, an approximately fixed switching frequency is achieved. However, the variation of the switching frequency with load current still exists. Through the implementation of the frequency compensation circuit, the switching frequency variation caused by the load current variation can be effectively reduced in order to obtaining a more fixed switching frequency. The adaptive on-time control regulator with frequency compensation has been successfully fabricated with 0.35 μm 30 V complementary double-diffused metal oxide semiconductor process and full chip test results are provided to verify the proposed method in this study.