Design of Fast Transient Response Voltage-Mode Buck Converter with Hybrid Feedforward and Feedback Technique

For a voltage-mode buck converter, to improve the transient response and reduce the size of the proportional-integral-differential (PID) compensation network, a hybrid feedforward and feedback technique (HFFT) is presented in this article. First, the HFFT utilizes the input voltage feedforward, the output voltage feedback, and the duty-ratio feedback to achieve fast line and load transient responses simultaneously. Second, the converter system is comprised of two feedback loops. One outer loop employs a voltage feedback control and provides a phase lead (PD) element. The other inner loop uses a duty-ratio feedback control and produces a phase lag (PI) element. Then adopting the PD and PI elements, a proposed implementation of PID compensation with small on-chip components can also be obtained. A buck converter chip with the HFFT has been fabricated in 0.18- $\mu \text{m}$ 1.8/5-V CMOS technology. Measurement results show that the output voltage of the buck converter is almost invariant under a line voltage step of 1.5 V and settled within $4.5~\mu \text{s}$ for a load current step of 500 mA.