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PDF LM2638 Data sheet ( Hoja de datos )
| Número de pieza | LM2638 | |
| Descripción | Motherboard Power Supply Solution with a 5-Bit Programmable Switching Controller and Two Linear Regulator Controllers | |
| Fabricantes | National Semiconductor | |
| Logotipo |  |
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May 1999
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™ 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 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 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 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.
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 ±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
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™ is a trademark of Cyrix Corporation a wholly owned subsidiary of National Semiconductor Corporation.
Pentium™ is a trademark of Intel Corporation.
K6™ is a trademark of Advanced Micro Devices, Inc.
© 1999 National Semiconductor Corporation DS101034
www.national.com
1 page  
Pin Description
Pin Pin Name
1 LG
2 PGND
3 VDD
4 SNS2
5 G2
6 SGND
7 VCC
8 SNS1
9 CS+
10 CS−
11 CP
12 FREQ
13 EAO
14 FB
15 PWGD
16 VID4
17 VID3
18 VID2
19 VID1
20 VID0
21 G3
22 SNS3
23 EN
24 HG
Pin Function
Low side N-FET gate driver output.
Ground for the two FET drivers of the switching section.
Supply for the FET gate drivers. Usually tied to +12V.
Feedback pin for the 1.5V linear regulator.
Gate drive output for the external N-MOS of the fast 1.5V linear regulator.
Ground for internal signal circuitry and system ground reference.
Supply voltage. Usually +5V.
Output voltage monitor input for the switching regulator.
Switching regulator current sense input, positive node.
Switching regulator current sense input, negative node.
Charge pump. Output is a square wave with 50% duty cycle. Amplitude is close to VCC
voltage.
Switching frequency adjustment pin. An external resistor is needed to set the desired
frequency.
Output of the error amplifier. Used for compensating the switching regulator.
Inverting input of the error amplifier. Used for compensating the switching regulator.
Open collector Power Good signal.
5-Bit DAC input, MSB.
5-Bit DAC input.
5-Bit DAC input.
5-Bit DAC input.
5-Bit DAC input, LSB.
Gate drive pin for the external N-MOS of the 1.25V linear regulator.
Feedback pin for the 1.25V linear regulator.
Output Enable. A logic low shuts the whole chip down.
High side N-FET gate driver output.
5 www.national.com
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| Páginas | Total 8 Páginas | |
| PDF Descargar | [ Datasheet LM2638.PDF ] | |
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