10/96

BLOCK DIAGRAM

•

Combined DAC/Voltage

Monitor and PWM Functions

•

4-Bit Digital-to-Analog

Converter (DAC)

•

1.0% DAC/Reference

•

Low Offset X20 Current Sense

Amplifier

•

100kHz, 200kHz, 400kHz

Oscillator Frequency Options

•

Foldback Current Limiting

•

Overvoltage and Undervoltage

Fault Windows

•

Undervoltage Lockout

•

2

Ω Totem Pole Output

•

Chip Disable Function

Pentium® Pro Controller

FEATURES

DESCRIPTION

UDG-96106-1

UCC2880-4/-5/-6

UCC3880-4/-5/-6

PRELIMINARY

The UCC3880-4/-5/-6 combines high precision reference and voltage monitor-

ing circuitry with average current mode PWM controller circuitry to power Intel

Pentium Pro and other high-end microprocessors with a minimum of external

components. The UCC3880-x converts 5VDC to an adjustable output, ranging

from 2.0VDC to 3.5VDC in 100mV steps with 1% DC system accuracy.

The chip includes a precision 5V reference which is capable of sourcing cur-

rent to an external load. The output voltage of the DAC is derived from this

reference, and is programmed directly by Intel’s VID pins (Table 1).

The accuracy of the DAC/reference combination is 1.0%. The overvoltage and

undervoltage comparators monitor the system output voltage and indicate

when it rises above or falls below its programmed value by more than 7.5%. A

second overvoltage protection comparator pulls the current amplifier output

voltage low to force zero duty cycle when the system output voltage exceeds

its designed value by more than 15%. This comparator also terminates the cy-

cle. Undervoltage lockout circuitry assures the correct logic states at the out-

puts during powerup and powerdown. Grounding the ENABLE pin forces the

GATE output low.

(continued)