4.4 A 10/30MHz Wide-duty-cycle-range buck converter with DDA-based Type-III compensator and fast reference-tracking responses for DVS applications

Abstract

Dynamic voltage scaling (DVS) is an effective strategy in reducing the power consumption of a processor through adjusting its supply voltage at runtime. The power converter that drives the processor should have a wide output voltage range and fast reference-tracking response while maintaining a high efficiency. For such applications, inductive switching converters are suitable candidates [1-4]. To enhance the transient response and to reduce the size of off-chip components, DC-DC converters switching in the 10MHz range are studied recently. When switching at a high frequency, efficiency is compromised as the switching loss becomes significant. Moreover, comparator delay of a few ns causes serious over-charging and over-discharging of the ramp capacitor and the delay also limits the maximum duty cycle of the converter. A current-mode control needs an on-chip current sensor that would consume too much power when running in the 10MHz range. In [5], a 5MHz converter employs auto-selectable peak- and valley-current control, but the duty cycle range is limited to 0.6. A higher switching frequency (f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">s</sub> ) would further reduce this range and would not be applicable for DVS. Therefore, a voltage-mode control with Type-III compensation for loop bandwidth extension becomes an attractive solution. However, a conventional Type-III compensator needs large on-chip compensation capacitors and resistors. In [6], a pseudo Type-III compensator reduces the value and thus size of those components, however, it requires adding lowpass and bandpass functions that complicates the design, and furthermore it does not use any special technique for fast reference tracking.