LM2636 National Semiconductor, LM2636 Datasheet

LM2636

Manufacturer Part Number

LM2636

Description

5-Bit Programmable Synchronous Buck Regulator Controller

Manufacturer

National Semiconductor

Datasheet

1.LM2636.pdf (14 pages)

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Download datasheet (326Kb)

LM2636

5-Bit Programmable Synchronous Buck Regulator

Controller

General Description

The LM2636 is a high speed controller designed specifically

for use in synchronous DC/DC buck converters for advance

d microprocessors. A 5-bit DAC accepts the VID code di-

rectly from the CPU and adjusts the output voltage from 1.3V

to 3.5V. It provides the power good, over-voltage protection,

and output enable features as required by Intel VRM speci-

fications. Current limiting is achieved by monitoring the volt-

age drop across the r

eliminates an expensive current sense resistor.

The LM2636 employs a fixed-frequency voltage mode PWM

architecture. To provide a faster response to a large and fast

load transient, two ultra-fast comparators are built in to moni-

tor the output voltage and override the primary control loop

when necessary. The PWM frequency is adjustable from 50

kHz to 1 MHz through an external resistor. The wide range of

PWM frequency gives the power supply designer the flexibil-

ity to make trade-offs between load transient response per-

formance, MOSFET cost and the overall efficiency. The

adaptive non-overlapping MOSFET gate drivers help avoid

any potential shoot-through problem while maintaining high

efficiency. BiCMOS gate drivers with rail-to-rail swing ensure

that no spurious turn-on occur. When only 5V is available, a

bootstrap structure can be employed to accommodate an

NMOS high side switch. The precision reference trimmed to

Typical Application

Pentium

™

is a trademark of Intel Corporation.

DS_ON

of the high side MOSFET, which

FIGURE 1. 5V to 1.3V–3.5V, 14A Power Supply

DS100834

2.5% over temperature is available externally for use by

other regulators. Dynamic positioning of load voltage, which

helps cut the number of output capacitors, can also be imple-

mented easily.

Features

n 1.3V to 3.5V 5-bit programmable output voltage

n Synchronous rectification

n Power Good flag and output enable

n Over-voltage protection

n Initial Output Accuracy: 1.5% over temperature

n Current limit without external sense resistor

n Adaptive non-overlapping MOSFET gate drives

n Adjustable switching frequency: 50 kHz to 1 MHz

n Dynamic output voltage positioning

n 1.256V reference voltage available externally

n Plastic SO-20 package and TSSOP-20 package

Applications

n Motherboard power supply/VRM for Cyrix Gxm, Cyrix

n 5V to 1.3V–3.5V high current power supplies

Gxi, Cyrix MII, Pentium

processors

™

II, Pentium Pro, 6x86 and K6

DS100834-1

October 1999

www.national.com

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