Description
Digital controllers have become an attractive choice in switching voltage regulators for low-cost, high performance applications such as microprocessor voltage regulation modules (VRM's) and portable electronicssuch as mobile phones and personal digital assistants (PDA's). This report discusses issues related to the use of digital control in pulse-width modulation (PWM) converters, with emphasis on VRM applications. The presence of steady-state limit cycles in digitally controlled PWM converters is analyzed, and conditions for their elimination are suggested. Digital dither is introduced as a means of increasing the effective resolution of digital PWM (DPWM) modules. VRM passive current sharing and transient response are discussed from the perspective of digital control. A VRM sensing scheme using a single low-resolution window analog-to-digital converter (ADC) is proposed. The above discussions are illustrated with simulations and experimental results.