A fast settling oversampled digital sliding-mode DC-DC converter

An all-digital sliding-mode (ADSM) controlled dc-dc converter, utilizing single-bit oversampled frequency domain digitizers in its feedback path is proposed. Sliding-mode control provides several benefits over the traditional PID control in terms of fast transient response, robustness to parameter and component variations, and low sensitivity to loop disturbances. However, analog implementations of sliding-mode control require several amplifiers in the controller and suffer from process, voltage, and temperature variations. In the proposed approach, the sliding-mode controller (SMC) is implemented digitally; utilizing a first order single-bit ΣΔ frequency to digital converter (ΣΔFDC)-based feedback and reference digitizing ADCs, running at 32-MHz sampling rate. The ADSM regulator achieves 1% settling time in less than 5 μs for a load variation of 600 mA. The SMC uses a high-bandwidth hysteretic differentiator and an integrator to perform the sliding control law in digital domain. The proposed approach overcomes the steady-state error (or dc offset), and band limits the switching frequency, which are the two common problems associated with SMCs. The IC is designed and fabricated on a 0.35-μm CMOS process occupying an active area of 2.72 mm².