Out in Front: November 9, 1995

Unitrode’s UC3886 PWM controller and UC3910 4-bit DAC and voltage monitor collaborate to power the Intel Pentium Pro P6 µP at its correct rail voltage. The P6 includes four internally set package pins that indicate, via binary code, what nominal value a device requires. Designers have to supply several amps of dc power at the indicated nominal rail voltage between 2.4 and 3.4V, according to the voltage grade of the CPU IC.

The Unitrode devices simplify the power-supply task by having the UC3910 DAC read the P6 nominal voltage code and generating a corresponding analog voltage in 16 steps from 2 to 3.5V with 1% accuracy. This voltage is the setpoint for the PWM controller IC, which provides a P6 supply rail from a 5V dc input, using a circuit that also includes an external N-channel MOSFET switch and passive components. The PWM controller has 3.5-MHz gain-bandwidth product amplifiers to support sudden changes in current demand, which can be as fast as going from idle to full power in 10 nsec.

The 4-bit DAC IC also contains a precision 5V (0.5%) reference output, which can source as much as 10 mA. For monitoring the supply rail to the CPU, the IC includes a programmable window comparator, which you can set as a percentage centered around the DAC output, and an overvoltage-protection comparator. A reference design and kit are available for the power-supply subsystem. Both ICs are available in 16-pin plastic DIP, ceramic DIP, and SOIC packages. The UC3886 PWM controller and UC3910 DAC and voltage monitor cost $2.30 and $2.21 (1000), respectively.
—by Bill Schweber

Unitrode Integrated Circuits Corp, Merrimack, NH. (603) 424-2410