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LM2638M-LM2638MX
Motherboard Power Supply Solution with a 5-Bit Programmable Switching Controller and Two Linear Regulator Controllers
LM2638
Motherboard Power Supply Solution witha 5-Bit
Programmable Switching Controller and Two Linear
Regulator Controllers
General DescriptionThe LM2638 providesa comprehensive embedded power
supply solutionfor motherboards hosting high performance
MPUs suchas Pentium™ II,MII™,K6™-2and other similar
high performance MPUs. The LM2638 incorporatesa 5-bit
programmable, synchronous buck switching controller and
two high-speed linear regulator controllersina 24-pinSO
package.Ina typical application,the switching controller
suppliesthe MPU core,andthe linear regulator controllers
supplythe GTL+busandthe clockor graphics chip core.A
charge pumppin helps providethe necessary voltageto
powerthe linear sections when12V isshutoff during system
standby suchas STR mode.
Switching Section— The switching regulator controllerfea-
turesan Intel-compatible, 5-bit programmable output volt-
age, over-currentand over-voltage protection,a power good
signal,anda logic-controlled output enable. Therearetwo
user-selectable over-current protection methods. One pro-
vides accurate over-current protectionwiththeuseofanex-
ternal sense resistor.The other savescostby taking advan-
tageofthe rDS_ONofthe high-side FET. When thereisan
over voltage,the controller turnsoffthe high side FETand
turnsonthelow side.
Linear Section— Thetwo linear regulator controllers fea-
ture wide control bandwidth, N-FETand NPN transistor driv-
ing capability andan adjustable output. The wide control
bandwidth makes meetingthe GTL+bus transient response
requirementan easyjob.In minimum configuration,thetwo
controllers defaultto 1.5Vand 1.25V respectively.
Both linear controllers have under voltage latch-off.
Features Provides3 regulated voltages Power Goodflagand output enable Charge pumppin
Switching Section Synchronous rectification 5-bit DAC programmable downto 1.3V Typical ±1% DAC tolerance Switching frequency:50kHzto1 MHz Over-voltage protection Two methodsof over-current protection Adaptive non-overlapping FET gate drives Soft start without external capacitor
Linear Section N-FETand NPN drive capability Ultrafast response speed Under voltage latch-offat 0.63V Output voltages defaultto 1.5Vand 2.5Vyet adjustable
Applications Embedded power suppliesfor motherboards Triple DC/DC power supplies Programmable high current DC/DC power supply
Pin ConfigurationMII™ isatrademarkofCyrixCorporationawholly owned subsidiaryof National Semiconductor Corporation.
Pentium™isatrademark ofIntelCorporation.
K6™isatrademark ofAdvancedMicro Devices,Inc.
24-Lead SOICDS101034-1
Top View
Order Number LM2638M
SeeNS Package Number M24BMay 1999
LM2638
Motherboard
Power
Supply
Solution
with
5-Bit
Programmable
Switching
Controller
and
Linear
Regulator
Controllers©1999 National Semiconductor Corporation DS101034
