The APW6021 provides the power control and protection for four output voltages in high-performance, graphics intensive microprocessor and computer applications. The IC integrates voltage-mode PWM controller and three linear controllers, as well as the monitoring and protection functions into a 28-pin SOIC package. The PWM controller regulates the microprocessor core voltage with a synchronous-rectified buck converter. The linear controllers regulate the computer system's AGP 1.5V or 3.3V bus power, the 1.5V GTL bus power, and the 1.8V power for the North/South Bridge core voltage and/or cache memory circuits. The APW6021 includes an Intelcompatible, TTL 5-input digital-to-analog converter (DAC) that adjusts the core PWM output voltage from 1.3 VDC to 2.05 VDC in 0.05V steps and from 2.1 VDC to 3.5 VDC in 0.1V increments. The precision reference and voltage-mode control provide 1 % s tatic regulation. The AGP bus power linear controller's output (VOUT2 ) is user-selectable, through a TTL-compatible signal applied at the SELECT pin, for levels of 1.5V or 3.3V with 3% accuracy. Based on the status of the FIX pin, the other two linear regulators provide either fixed output voltages of 1.5V 3% (VOUT3 ) and 1.8V3% (VOUT4 ), or user-adjustable by means of an external resistor divider. All linear controllers can employ either N-channel MOSFETs or bipolar NPNs for the pass transistor.