
REV. A
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use, nor for any infringements of patents or other rights of third parties
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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
6
1% 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
20k
V
V
OLDO1
1
m
F
V
INLDO1
Q
LDO1
R3
V
CC
+12V
1
m
F
22
m
F
V
IN
+5V
+
C
IN
L
+C
O
V
1.3V TO
3.5V
R
SENSE
1nF
C
COMP
CMP
ADP3155
R2
R1
150pF
V
CC
SD
DRIVE1
SENSE+
SENSE–
DRIVE2
PGND
AGND
C
T
FB1
V
LDO1
VID0–VID4
5-BIT CODE
Q1
Q2
R6
20k
V
V
OLDO2
1
m
F
V
INLDO2
Q
LDO2
FB2
V
LDO2
R5
Figure 1. Typical Application
FUNCTIONAL BLOCK DIAGRAM
CMPI
V
T1
V
REF
+5%
V
–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
VID0
VID2
VID3
VID4
ADP3155
AGND
VID1