Compensation Circuit Design Considerations for high Frequency DC/DC Buck Converters with Ceramic Output Capacitors

Modern power applications are driving the demand for power supply systems with fast transient response. This requires high bandwidth in addition to a robust system. The latest technology allows designing very high switching frequency (in the MHz range) DC-DC converters using ceramic capacitors as an output filter. Using traditional linear control will limit the maximum achievable bandwidth, and using the recently proposed non-linear control circuits will make the control circuit more complex and not as robust. This paper introduces loop compensation circuit design methods suitable for DC-DC converters operating at high switching frequencies (FSW > 1MHz), which are higher than the output capacitor's resonant frequency (FR ≈ 1-2MHz). These developments are introduced in the context of the design and experimental evaluation of a 5 MHz DC-DC Buck converter. Special emphasis is placed on key design compensation circuits using the Error Amplifier as an active element in addition to the passive elements that are combined to present an improved novel active linear control scheme.