Dual Power Supply Controller
for Desktop Systems
a
ADP3156
FEATURES
FUNCTIONAL BLOCK DIAGRAM
Active Voltage Positioning with Gain and Offset
Adjustment
AGND
V
DRIVE1 DRIVE2 PGND
SENSE+ SENSE–
PWRGD
CC
Optimal Compensation for Superior Load Transient
Response
DELAY
+15%
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
NONOVERLAP
V
DRIVE
REF
SD
2R
CROWBAR
OFF
IN
V
+5% V
–5%
REF
REF
CMPI
Overvoltage Protection Crowbar Protects Loads with
No Additional External Components
Power Good Output
V
T1
S
Q
R
R
V
REF
g
SO-16 Package
m
V
T2
REFERENCE
APPLICATIONS
V
LDO
C
T
Desktop Computer Supplies
ACPI-Compliant Power Systems
General Purpose DC-DC Converters
CMPT
1.20V
FB
V
OFF-TIME
CONTROL
IN
ADP3156
SENSE–
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® III and other high performance processor
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.
CMP
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.
V
+12V
CC
V
+5V
IN
C
+
IN
22F
1F
R1
V
CC
SD
DRIVE1
V
LDO
L
RSENSE
V
V
O2
ADP3156
SENSE+
O
35k⍀
+
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%.
1000F
FB
C
O
1nF
20k⍀
CMP
SENSE–
DRIVE2
R2
CCOMP
C
T
200pF
AGND PGND
Figure 1. Typical Application
Pentium is a registered trademark of Intel Corporation.
All other trademarks are the property of their respective holders.
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.
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© Analog Devices, Inc., 1999