A monolithic 2nd-order boundary controller for buck converter with fast transient response

It is well known from control theory that 2^nd-order boundary control is able to achieve a faster transient response over the conventional hysteretic control. However, no available monolithic 2^nd-order boundary controller for buck converter has not been found. The main challenges of designing this controller are the implementation of the non-invasion output capacitor current sensor and the hardware calculation of both positive and negative squared terms in the 2^nd-boundary control law. This paper overcomes those challenges and successfully designed and fabricated the controller with a standard 0.35μm CMOS process. Measurement results show that, during a 400mA load current step change, the controller is able to regulate a 4MHz buck converter output voltage to return to its nominal value within one ON/OFF switching action (1μs) with less than 50mV overshoot/undershoot. The measured highest power efficiency is about 94%.