A programmable integrated digital controller for a buck converter is presented. It consists of three major components: (1) a VCO (voltage controlled oscillator) driving a counter to serve as an ADC (analog to digital converter); (2) a Proportional, Integral and Derivative (PID) compensator that employs a variable integration time technique in enhancing accuracy and stability; and (3) a dual-band switching PWM generator with a modified tapped delay line for better output resolution and area efficiency. ²...[ Read more ]

A programmable integrated digital controller for a buck converter is presented. It consists of three major components: (1) a VCO (voltage controlled oscillator) driving a counter to serve as an ADC (analog to digital converter); (2) a Proportional, Integral and Derivative (PID) compensator that employs a variable integration time technique in enhancing accuracy and stability; and (3) a dual-band switching PWM generator with a modified tapped delay line for better output resolution and area efficiency.

The controller was simulated using Matlab in the system level and Hspice in the transistor level. A novel mixed-signal simulation strategy in enhancing simulation speed is discussed. The chip is fabricated in a 0.6μ CMOS n-well process and the controller occupies an area of 0.6x1.3mm². The converter switches at 1 MHz, while the VCO switches from 10MHz to 80MHz. Measurement results show that the proposed controller is able to regulate the output voltage from 0.2V (low voltage band) to 3V (high voltage band) with a supply voltage of 3.3V. The measured output ripple voltages was smaller than 20mV. Transient responses can be programmed by changing the coefficients of the PID controller. A settling time of 70μs for a step change of 2V is achievable, and an efficiency of over 80% is achieved over wide operating conditions.