鈩?/div>
-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.
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
Switching Section
n
Synchronous rectification
n
5-bit DAC programmable down to 1.3V
n
Typical
鹵
1% DAC tolerance
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
Linear Section
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
Switching Section
鈥?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
DS_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
鈥?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.
Applications
n
Embedded power supplies for motherboards
n
Triple DC/DC power supplies
n
Programmable high current DC/DC power supply
Pin Configuration
24-Lead SOIC
DS101034-1
Top View
Order Number LM2638M
See NS Package Number M24B
M II
鈩?/div>
is a trademark of Cyrix Corporation a wholly owned subsidiary of National Semiconductor Corporation.
Pentium
鈩?/div>
is a trademark of Intel Corporation.
K6
鈩?/div>
is a trademark of Advanced Micro Devices, Inc.
漏 1999 National Semiconductor Corporation
DS101034
www.national.com
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