REV. A

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a

ADP3154

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 Dual Power Supply

FUNCTIONAL BLOCK DIAGRAM

CMPI

DELAY

PWRGD

SENSE+

CROWBAR

OFF

IN

NONOVERLAP

DRIVE

Q

S

R

DRIVE1 DRIVE2 PGND

2R

SENSE–

SD

VLDO

CMPT

R

REFERENCE

DAC

OFF-TIME

CONTROL

SENSE–

1.20V

CMP

FB

VID0

VID2

VID3

VID4

ADP3154

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

Onboard Linear Regulator Controller

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

TSSOP-20 Package

APPLICATIONS

Desktop PC Power Supplies for:

Pentium II and Pentium III Processor Families

AMD-K6 Processors

VRM Modules

GENERAL DESCRIPTION

The ADP3154 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 ADP3154 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 ADP3154 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 ADP3154 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%.

The ADP3154 contains a linear regulator controller that is

designed to drive an external N-channel MOSFET. This linear

regulator is used to generate the auxiliary voltages (AGP, GTL,

etc.) required in most motherboard designs, and has been de-

signed to provide a high bandwidth load-transient response. A

pair of external feedback resistors sets the linear regulator out-

put voltage.

1 F

22 F

+

L

+

1.3V TO

3.5V

1nF

C

COMP

35k

20k

1000 F

R1

200pF

SD

DRIVE1

SENSE+

SENSE–

DRIVE2

PGND

AGND

CMP

ADP3154

FB

VLDO

R2

VID0–VID4

5-BIT CODE

Figure 1. Typical Application

Pentium is a registered trademark of Intel Corporation.

All other trademarks are the property of their respective holders.