a
5-Bit Programmable Synchronous
Controller for Pentium® III Processors
ADP3157
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
FUNCTIONAL BLOCK DIAGRAM
AGND
VCC DRIVE1 DRIVE2 PGND
SENSE+ SENSE–
PWRGD
DELAY
NONOVERLAP
DRIVE
SD
VREF +15%
2R
CROWBAR
IN
VREF +5% VREF –5%
CMPI
S
Q
VT1
R
gm
VT2
CT
R
VREF
REFERENCE
1.20V
CMPT
OFF-TIME
CONTROL
VID0
SENSE–
VID1
VID2
GENERAL DESCRIPTION
The ADP3157 is a highly efficient synchronous buck switching
regulator controller optimized for converting the 5 V main supply 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 Nchannel 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.
VID3
ADP3157
CMP
VCC +12V
22F
1F
VIN +5V
CIN
+
VCC
DRIVE1
SD
L
R1
The ADP3157 provides accurate and reliable short circuit protection and adjustable current limiting. It also includes an
integrated overvoltage crowbar function to protect the microprocessor from destruction in case the core supply exceeds the
nominal programmed voltage by more than 15%.
CMP
R2
RSENSE
VO
1.3V TO
3.5V
ADP3157
+
SENSE+
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.
VID4
DAC
CCOMP
150pF
1nF
CO
SENSE–
CT
DRIVE2
AGND
PGND
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.
REV. A
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.
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
