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
Controller for Pentium
®
III Processors
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 61% 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
20kV
V
OLDO1
1mF
V
INLDO1
Q
LDO1
R3
V
CC
+12V
1mF22mF
V
IN
+5V
+
C
IN
L
+
C
O
V
O
1.3V TO
3.5V
R
SENSE
1nF
C
COMP
CMP
R2
R1
150pF
V
CC
SD
DRIVE1
SENSE+
SENSE–
DRIVE2
PGND
AGND
C
T
ADP3155
FB1
V
LDO1
VID0–VID4
5-BIT CODE
Q1
Q2
R6
20kV
V
OLDO2
1mF
V
INLDO2
Q
LDO2
FB2
V
LDO2
R5
CMP
Figure 1. Typical Application
FUNCTIONAL BLOCK DIAGRAM
CMPI
V
T1
V
REF
+5%
V
REF
–5%
DELAY
V
REF
+15%
PWRGD SENSE+
CROWBAR
OFF
IN
NONOVERLAP
DRIVE
Q
S
R
DRIVE1 DRIVE2 PGND
2R
SENSE–
VLDO1
REFERENCE
FB1
VLDO2
FB2
V
REF
V
CC
SD
V
T2
CMPT
C
T
g
m
R
DAC
OFF-TIME
CONTROL
V
IN
SENSE–
1.20V
CMP
VID0VID2VID3VID4
ADP3155
AGND
VID1