lm2638m National Semiconductor Corporation, lm2638m Datasheet

lm2638m

Manufacturer Part Number

lm2638m

Description

Motherboard Power Supply Solution With A 5-bit Programmable Switching Controller And Two Linear Regulator Controllers

Manufacturer

National Semiconductor Corporation

Datasheet

1.LM2638M.pdf (8 pages)

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LM2638

Motherboard Power Supply Solution with a 5-Bit

Programmable Switching Controller and Two Linear

Regulator Controllers

General Description

The LM2638 provides a comprehensive embedded power

supply solution for motherboards hosting high performance

MPUs such as Pentium

high performance MPUs. The LM2638 incorporates a 5-bit

programmable, synchronous buck switching controller and

two high-speed linear regulator controllers in a 24-pin SO

package. In a typical application, the switching controller

supplies the MPU core, and the linear regulator controllers

supply the GTL+ bus and the clock or graphics chip core. A

charge pump pin helps provide the necessary voltage to

power the linear sections when 12V is shut off during system

standby such as STR mode.

Switching Section — The switching regulator controller fea-

tures an Intel-compatible, 5-bit programmable output volt-

age, over-current and over-voltage protection, a power good

signal, and a logic-controlled output enable. There are two

user-selectable over-current protection methods. One pro-

vides accurate over-current protection with the use of an ex-

ternal sense resistor. The other saves cost by taking advan-

tage of the r

over voltage, the controller turns off the high side FET and

turns on the low side.

Linear Section — The two linear regulator controllers fea-

ture wide control bandwidth, N-FET and NPN transistor driv-

ing capability and an adjustable output. The wide control

bandwidth makes meeting the GTL+ bus transient response

requirement an easy job. In minimum configuration, the two

controllers default to 1.5V and 1.25V respectively.

Pin Configuration

M II

Pentium

™

is a trademark of Advanced Micro Devices, Inc.

is a trademark of Cyrix Corporation a wholly owned subsidiary of National Semiconductor Corporation.

™

is a trademark of Intel Corporation.

DS_ON

of the high-side FET. When there is an

™

II, M II

™

, K6

™

DS101034

-2 and other similar

See NS Package Number M24B

Order Number LM2638M

24-Lead SOIC

Top View

Both linear controllers have under voltage latch-off.

Features

n Provides 3 regulated voltages

n Power Good flag and output enable

n Charge pump pin

n Synchronous rectification

n 5-bit DAC programmable down to 1.3V

n Typical

n Switching frequency: 50 kHz to 1 MHz

n Over-voltage protection

n Two methods of over-current protection

n Adaptive non-overlapping FET gate drives

n Soft start without external capacitor

n N-FET and NPN drive capability

n Ultra fast response speed

n Under voltage latch-off at 0.63V

n Output voltages default to 1.5V and 2.5V yet adjustable

Applications

n Embedded power supplies for motherboards

n Triple DC/DC power supplies

n Programmable high current DC/DC power supply

DS101034-1

Switching Section

Linear Section

1% DAC tolerance

www.national.com

May 1999

Related parts for lm2638m

lm2638m Summary of contents

Page 1

... Ultra fast response speed n Under voltage latch-off at 0.63V n Output voltages default to 1.5V and 2.5V yet adjustable Applications n Embedded power supplies for motherboards n Triple DC/DC power supplies n Programmable high current DC/DC power supply 24-Lead SOIC DS101034-1 Top View Order Number LM2638M See NS Package Number M24B May 1999 www.national.com ...

Page 2

Absolute Maximum Ratings If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications Junction Temperature Power Dissipation (Note 2) Electrical Characteristics = T = +25˚C. Limits appearing in ...

Page 3

Electrical Characteristics = T = +25˚C. Limits appearing in boldface type apply over the 0˚C to +70˚C range. (Continued) plain type apply for Symbol Parameter SWITCHING SECTION V PWGD High Trip Point PWGD_HI V PWGD Low Trip ...

Page 4

Electrical Characteristics = T = +25˚C. Limits appearing in boldface type apply over the 0˚C to +70˚C range. (Continued) plain type apply for ± 12V = 25˚C, Test Mode ...

Page 5

Pin Description Pin Pin Name 1 LG Low side N-FET gate driver output. 2 PGND Ground for the two FET drivers of the switching section Supply for the FET gate drivers. Usually tied to +12V SNS2 ...

Page 6

Block Diagram Test Circuit www.national.com FIGURE 1. LDO Controller Test Circuit 6 DS101034-3 DS101034-4 ...

Page 7

Typical Application 7 www.national.com ...

Page 8

... National does not assume any responsibility for use of any circuitry described, no circuit patent licenses are implied and National reserves the right at any time without notice to change said circuitry and specifications. 24-Lead Small Outline Package Order Number LM2638M NS Package Number M24B 2. A critical component is any component of a life ...

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