LM2688

Non-synchronous Step-down Controller for Pentium

Microprocessors

General Description

The LM2688 is a low-cost non-synchronous voltage-mode

PWM controller which maintains an accurate and adjustable

output voltage for high current, low voltage DC/DC applica-

tions such as the Pentium microprocessor family. By using

different combinations of feedback resistors, the regulator

output voltage can be precisely adjusted to match different

requirements. Coming in an 8-lead surface mount package,

the LM2688 can be used to control a buck regulator with an

load current up to 10A. An on-chip precision trimmed refer-

ence allows tight voltage regulation and an internal 150 kHz

fixed-frequency oscillator eliminates extra components to set

the switching frequency. The LM2688 also provides an ON/

OFF pin which enables the CPU to shutdown the regulator

when necessary. Self protection features include a two stage

current limit for the output switch and an over temperature

shutdown for complete protection under fault conditions. The

controller also provides internal loop gain compensation,

minimizing the number of external components.

Features

n

Adjustable output voltage

n

Available in 8-pin surface mount

n

Guaranteed 0.5A gate drive current

n

Supply voltage up to 40V

n

150 kHz fixed frequency internal oscillator

n

TTL shutdown capability

n

Low power standby mode, I

n

Thermal shutdown and current limit protection

Applications

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Controller for voltage regulators for Pentium, Pentium

MMX, K5, K6 MMX, Alpha and PowerPC processors

n

Efficient pre-regulator for linear regulators

Typical Application

Pentium Processor Power Supply

DS100050-1

For more information about the above application, please refer to the Application Hints section.

July 1997

© 1997 National Semiconductor Corporation

DS100050

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