OBSOLETE
LM2638
www.ti.com
SNVS046A –MAY 2004–REVISED NOVEMBER 2004
LM2638 Motherboard Power Supply Solution with a 5-Bit Programmable Switching
Controller and Two Linear Regulator Controllers
Check for Samples: LM2638
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FEATURES
– Linear Section
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N-FET and NPN drive capability
Ultra fast response speed
2345
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Provides 3 regulated voltages
Power Good flag and output enable
Charge pump pin
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Under voltage latch-off at 0.63V
Output voltages default to 1.5V and 2.5V yet
adjustable
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Switching Section
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Synchronous rectification
5-bit DAC programmable down to 1.3V
Typical ±1% DAC tolerance
APPLICATIONS
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Embedded power supplies for motherboards
Triple DC/DC power supplies
Switching frequency: 50 kHz to 1 MHz
Over-voltage protection
Programmable high current DC/DC power
supply
Two methods of over-current protection
Adaptive non-overlapping FET gate drives
Soft start without external capacitor
DESCRIPTION
The LM2638 provides a comprehensive embedded power supply solution for motherboards hosting high
performance MPUs such as Pentium™ II, M II™, K6™-2 and other similar 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 features an Intel-compatible, 5-bit programmable output
voltage, 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 provides accurate over-current protection
with the use of an external sense resistor. The other saves cost by taking advantage of the rDS_ON of the high-
side FET. When there is an over voltage, the controller turns off the high side FET and turns on the low side.
Linear Section — The two linear regulator controllers feature wide control bandwidth, N-FET and NPN transistor
driving 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.
Both linear controllers have under voltage latch-off.
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Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of
Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.
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K6 is a trademark of Advanced Micro Devices, Inc..
M II is a trademark of Cyrix Corporation.
Pentium is a trademark of Intel Corporation.
All other trademarks are the property of their respective owners.
PRODUCTION DATA information is current as of publication date.
Products conform to specifications per the terms of the Texas
Instruments standard warranty. Production processing does not
necessarily include testing of all parameters.
Copyright © 2004, Texas Instruments Incorporated