REV. A

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a

ADP3157

One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.

Tel: 781/329-4700

World Wide Web Site: http://www.analog.com

Fax: 781/326-8703

© Analog Devices, Inc., 1999

5-Bit Programmable Synchronous

FUNCTIONAL BLOCK DIAGRAM

CMPI

DELAY

PWRGD

SENSE+

CROWBAR

IN

NONOVERLAP

DRIVE

Q

S

R

DRIVE1 DRIVE2 PGND

2R

SENSE–

SD

CMPT

R

REFERENCE

DAC

OFF-TIME

CONTROL

SENSE–

1.20V

CMP

VID0

VID2

VID3

VID4

ADP3157

AGND

VID1

FEATURES

Active Voltage Positioning with Gain and Offset

Adjustment

Optimal Compensation for Superior Load Transient

Response

VRM 8.2, VRM 8.3 and VRM 8.4 Compliant

5-Bit Digitally Programmable 1.3 V to 3.5 V Output

Dual N-Channel Synchronous Driver

Total Output Accuracy

1% Over Temperature

High Efficiency, Current-Mode Operation

Short Circuit Protection

Overvoltage Protection Crowbar Protects Microprocessors

with No Additional External Components

Power Good Output

SO-16 Package

APPLICATIONS

Desktop PC Power Supplies for:

Pentium II and Pentium III Processor Families

AMD-K6 Processors

VRM Modules

GENERAL DESCRIPTION

The ADP3157 is a highly efficient synchronous buck switching

regulator controller optimized for converting the 5 V main sup-

ply into the core supply voltage required by the Pentium III and

other high performance processors. The ADP3157 uses an

internal 5-bit DAC to read a voltage identification (VID) code

directly from the processor, which is used to set the output

voltage between 1.3 V and 3.5 V. The ADP3157 uses a current

mode, constant off-time architecture to drive two external N-

channel MOSFETs at a programmable switching frequency that

can be optimized for size and efficiency. It also uses a unique

supplemental regulation technique called active voltage position-

ing to enhance load transient performance.

Active voltage positioning results in a dc/dc converter that meets

the stringent output voltage specifications for Pentium II and

Pentium III processors, with the minimum number of output

capacitors and smallest footprint. Unlike voltage-mode and

standard current-mode architectures, active voltage positioning

adjusts the output voltage as a function of the load current so that

it is always optimally positioned for a system transient.

The ADP3157 provides accurate and reliable short circuit pro-

tection and adjustable current limiting. It also includes an

integrated overvoltage crowbar function to protect the micro-

processor from destruction in case the core supply exceeds the

nominal programmed voltage by more than 15%.

1 F

22 F

+

L

+

1.3V TO

3.5V

1nF

C

COMP

R1

150pF

SD

DRIVE1

SENSE+

SENSE–

DRIVE2

PGND

AGND

CMP

ADP3157

R2

VID0–VID4

5-BIT CODE

Figure 1. 5-Bit Code Typical Application

Pentium is a registered trademark of Intel Corporation.

All other trademarks are the property of their respective holders.