LTC1553
5-Bit Programmable
Synchronous Switching
Regulator Controller for
Pentium
®
II Processor
FEATURES
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DESCRIPTION
The LTC
®
1553 is a high power, high efficiency switching
regulator controller optimized for 5V or 12V input to 1.8V-
3.5V output applications. It features a digitally programmable
output voltage, a precision internal reference and an internal
feedback system that provides output accuracy of
±1.5%
at
room temperature and typically
±2%
over-temperature, load
current and line voltage shifts. The LTC1553 uses a synchro-
nous switching architecture with two external N-channel
output devices, providing high efficiency and eliminating the
need for a high power, high cost P-channel device. Addition-
ally, it senses the output current across the on-resistance of
the upper N-channel FET, providing an adjustable current
limit without an external low value sense resistor.
The LTC1553 free-runs at 300kHz and can be synchronized
to a faster external clock if desired. It includes all the inputs
and outputs required to implement a power supply conform-
ing to the
Intel Pentium
®
II Processor VRM 8.2 DC/DC
Converter Specification.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Pentium is a registered trademark of Intel Corporation.
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5-Bit Digitally Programmable 1.8V to 3.5V Fixed
Output Voltage
Provides All Features Required by the
Intel
Pentium
®
II Processor VRM 8.2 DC/DC
Converter Specification
Flags for Power Good, Over-Temperature and
Overvoltage Fault
19A Output Current Capability from a 5V or 12V Supply
Dual N-Channel MOSFET Synchronous Driver
Initial Output Accuracy:
±1.5%
Excellent Output Accuracy:
±2%
Typ Over Line,
Load and Temperature Variations
High Efficiency: Over 95% Possible
Adjustable Current Limit Without External Sense
Resistors
Fast Transient Response
Available in 20-Lead SSOP and SW Packages
APPLICATIONS
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Power Supply for Pentium II, SPARC, ALPHA and
PA-RISC Microprocessors
High Power 5V or 12V to 1.8V-3.5V Regulators
TYPICAL APPLICATION
+
0.1µF
5.6k
5.6k
5.6k
V
CC
I
MAX
10µF
2.7k
PV
CC
12V
V
IN
5V
+
0.1µF
10µF
PWRGD
PENTIUM II
SYSTEM
®
PV
CC
G1
20Ω
Q1*
L
O
†
2µH
18A
C
OUT
††
330µF
×
7
V
OUT
1.8V TO
3.5V
14A
FAULT
5
OT
VID0 TO VID4
OUTEN
COMP
C1
150pF
R
C
8.2k
C
C
0.01µF
SS
SGND
GND
SENSE
LTC1553
I
FB
G2
Q2*
C
SS
0.1µF
0.1µF
*SILICONIX SUD50N03-10
**SANYO 10MV1200GX
†
COILTRONICS CTX02-13198 OR
PANASONIC 12TS-2R5SP
††
AVX TPSE337M006R0100
Figure 1. 5V to 1.8V-3.5V Supply Application
U
U
U
+
C
IN
**
1200µF
×
4
+
1553 F01
1
LINER [ LINEAR TECHNOLOGY ]
