A DC–DC Converter for a Fully Integrated PID Compensator With a Single Capacitor

In this brief, proportional-integral-derivative (PID) compensation with a single capacitor for a fully integrated controller employed in a direct DC-DC converter operating in a voltage mode is presented. To make up a compact-area on-chip controller, a novel compensator is proposed, utilizing the AC ripple current of the inductor, which enables the PID controller to be implemented with only one capacitor and one resistor. The converter runs not only in a continuous conduction mode (CCM) but also in a discontinuous conduction mode (DCM). The bandwidth of the overall loop is 120-200 kHz, which supports a fast transient response at a switching frequency of 1 MHz. The stability of the loop is guaranteed by theoretical analysis and experimental results to validate the proposed concept. The settling time is less than 85 μs at a load change of 1 A, and overshoot/undershoot voltages are within 50 mV. The buck converter with an input of 3.6 V and an output of 2.5 V for a maximum power of 3.125 W is fabricated in the 0.35-μm CMOS process, occupying a die area of 0.75 mm².