Multi-loop buck regulator for wide programmable switching frequency

This paper presents a multi-loop voltage-controlled buck converter that operates at a wide range of programmable switching frequency and works over an input voltage range of 3.5 V to 60 V and load current up to 3 A. The output voltage can be externally set between 0.9 V and 20 V. A major challenge was incorporating line feed-forward technique while having a programmable switching frequency between 200 KHz and 2 MHz. A design technique to implement this feature, low-power mode detection using zero-cross detector, and multi-loop control to improve transient response will be presented. The converter fabricated in 0.5 mum process consumes 60 muA in low-power mode.