5-Bit Programmable Synchronous
Controller for Pentium® III Processors
Active Voltage Positioning with Gain and Offset
Optimal Compensation for Superior Load Transient
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
Desktop PC Power Supplies for:
Pentium II and Pentium III Processor Families
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%.
FUNCTIONAL BLOCK DIAGRAM
VCC DRIVE1 DRIVE2 PGND AGND PWRGD SENSE+ SENSE–
VREF +5% VREF –5%
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.
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
© Analog Devices, Inc., 1999