LM2639

5-Bit Programmable, High Frequency Multi-phase PWM

Controller

General Description

The LM2639 provides an attractive solution for power sup-

sients. Compared to a conventional single-phase supply, an

LM2639 based multi-phase supply distributes the thermal

and electrical loading among components in multiple phases

and greatly reduces the corresponding stress in each com-

ponent. The LM2639 can be programmed to control either a

3-phase converter or a 4-phase converter. Phase shift

among the phases is 120˚ in the case of three phase and 90˚

with four-phase. Because the power channels are out of

phase, there can be significant ripple cancellation for both

the input and output current, resulting in reduced input and

output capacitor size. Due to the nominal operating fre-

quency of 2 MHz per phase, the size of the output inductors

can be greatly reduced which results in a much faster load

transient response and a dramatically shrunk output capaci-

tor bank. Microprocessor power supplies with all surface

mount components can be easily built.

The internal high speed transconductance amplifier guaran-

tees good dynamic performance. The output drive voltages

can be adjusted through a resistor divider to control switch-

ing loss in the external FETs.

The internal master clock frequency of up to 8 MHz is set by

an external reference resistor. An external clock of 10 MHz

can also be used to drive the chip to achieve frequency con-

trol and multi-chip operation.

The LM2639 also provides input under-voltage lock-out with

hysteresis and input over-current protection.

Features

n

Ultra fast load transient response

n

Enables all surface-mount-design

n

Selectable 2, 3, 4 phase operation

n

Clock frequency from 40 kHz to 10 MHz

n

Precision load current sharing

n

5-bit programmable from 3.5V to 1.3V

n

VID code compatible to VRM 8.X specification

n

Output voltage is 2.0V for VID code 11111

n

Selectable internal or external clock

n

Digital 16-step soft start

n

Input under-voltage lock-out, over-current protection

Applications

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Servers and workstations

n

High current, ultra-fast transient microprocessors

Pin Configuration

24-Pin Plastic SOIC

DS101143-1

Top View

See NS Package Number M24B

February 2000

© 2000 National Semiconductor Corporation

DS101143

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