REV. A

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a

ADP3155

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 Triple Power Supply

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

Two Onboard Linear Regulator Controllers

Total Output Accuracy

1% Over Temperature

High Efficiency, Current-Mode Operation

Short Circuit Protection

Overvoltage Protection Crowbar Protects Micro-

processors, with No Additional External Components

Power Good Output

TSSOP-20 Package

APPLICATIONS

Desktop PC Power Supplies for:

Pentium II and Pentium III Processor Families

AMD-K6 Processors

VRM Modules

Pentium is a registered trademark of Intel Corporation.

All other trademarks are the property of their respective holders.

GENERAL DESCRIPTION

The ADP3155 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 ADP3155 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 ADP3155 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 the 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 ADP3155 provides accurate and reliable short circuit pro-

tection and adjustable current limiting. It also includes an inte-

grated overvoltage crowbar function to protect the microprocessor

from destruction in case the core supply exceeds the nominal

programmed voltage by more than 15%.

The ADP3155 contains two linear regulator controllers that are

designed to drive external N-channel MOSFETs. These linear

regulators are used to generate the auxiliary voltages (AGP,

GTL, etc.) required in most motherboard designs, and have

been designed to provide a high bandwidth load-transient re-

sponse. A pair of external feedback resistors sets each linear

regulator output voltage.

R4

20k

1 F

R3

1 F

22 F

+

L

+

1.3V TO

3.5V

1nF

C

COMP

CMP

R2

R1

150pF

SD

DRIVE1

SENSE+

SENSE–

DRIVE2

PGND

AGND

ADP3155

FB1

VID0–VID4

5-BIT CODE

Q1

Q2

R6

20k

1 F

FB2

R5

CMP

Figure 1. Typical Application

FUNCTIONAL BLOCK DIAGRAM

CMPI

+5%

–5%

DELAY

+15%

PWRGD

SENSE+

CROWBAR

OFF

IN

NONOVERLAP

DRIVE

Q

S

R

DRIVE1 DRIVE2 PGND

2R

SENSE–

VLDO1

REFERENCE

FB1

VLDO2

FB2

SD

CMPT

R

DAC

OFF-TIME

CONTROL

SENSE–

1.20V

CMP

VID0

VID2

VID3

VID4

ADP3155

AGND

VID1