LM2638 National Semiconductor, LM2638 Datasheet
LM2638
Manufacturer Part Number
LM2638
Description
Motherboard Power Supply Solution with a 5-Bit Programmable Switching Controller and Two Linear Regulator Controllers
Manufacturer
National Semiconductor
Datasheet
1.LM2638.pdf
(8 pages)
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© 1999 National Semiconductor Corporation
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
K6
™
™
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
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