REV. 0

Information furnished by Analog Devices is believed to be accurate and

reliable. However, no responsibility is assumed by Analog Devices for its

use, nor for any infringements of patents or other rights of third parties

which may result from its use. No license is granted by implication or

otherwise under any patent or patent rights of Analog Devices.

a

ADP3156

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

Dual Power Supply Controller

for Desktop Systems

FUNCTIONAL BLOCK DIAGRAM

CMPI

DELAY

PWRGD

SENSE+

CROWBAR

OFF

IN

NONOVERLAP

DRIVE

Q

S

R

DRIVE1 DRIVE2 PGND

2R

SENSE–

SD

CMPT

R

REFERENCE

OFF-TIME

CONTROL

SENSE–

1.20V

CMP

FB

ADP3156

AGND

FEATURES

Active Voltage Positioning with Gain and Offset

Adjustment

Optimal Compensation for Superior Load Transient

Response

Fixed 1.5 V, 1.8 V and 2.5 V Output Versions

Dual N-Channel Synchronous Driver

On-Board Linear Regulator Controller

Total Output Accuracy

1% Over Temperature

High Efficiency, Current-Mode Operation

Short Circuit Protection

Overvoltage Protection Crowbar Protects Loads with

No Additional External Components

Power Good Output

SO-16 Package

APPLICATIONS

Desktop Computer Supplies

ACPI-Compliant Power Systems

General Purpose DC-DC Converters

GENERAL DESCRIPTION

The ADP3156 is a highly efficient synchronous buck switching

regulator controller optimized for converting the 3.3 V or 5 V

main supply into lower supply voltages required on the mother-

boards of Pentium

systems. The ADP3156 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 positioning to enhance load

transient performance. Active voltage positioning results in a

DC/DC converter that provides the best possible transient re-

sponse using 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 ADP3156 provides accurate and reliable short circuit

protection 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%.

Pentium is a registered trademark of Intel Corporation.

All other trademarks are the property of their respective holders.

1 F

22 F

+

L

+

1nF

C

COMP

35k

20k

1000 F

R1

200pF

SD

DRIVE1

SENSE+

SENSE–

DRIVE2

PGND

AGND

CMP

ADP3156

FB

R2

Figure 1. Typical Application

The ADP3156 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.