LTC1736
5-Bit Adjustable
High Efficiency Synchronous
Step-Down Switching Regulator
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FEATURES
DESCRIPTIO
The LTC®1736 is a synchronous step-down switching
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Dual N-Channel MOSFET Synchronous Drive
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Synchronizable/Programmable Fixed Frequency
Wide VIN Range: 3.5V to 36V Operation
regulator controller optimized for CPU power. The output
voltage is programmed by a 5-bit digital-to-analog con-
verter (DAC) that adjusts the output voltage from 0.925V
to 2.00V according to Intel mobile VID specifications. The
0.8V reference is compatible with future microprocessor
generations.
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5-Bit Digital-to-Analog VOUT Selection:
0.925V to 2.00V Range with 50mV/25mV Steps
OPTI-LOOPTM Compensation Minimizes COUT
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±
1% Output Voltage Accuracy
Power Good Output Voltage Monitor
Active Voltage Positioning Compatible
Output Overvoltage Crowbar Protection
Internal Current Foldback
The operating frequency (synchronizable up to 500kHz) is
set by an external capacitor allowing maximum flexibility
inoptimizingefficiency.Theoutputvoltageismonitoredby
a power good window comparator that indicates when the
output is within 7.5% of its programmed value.
Latched Short-Circuit Shutdown Timer
with Defeat Option
Forced Continuous Control Pin
Optional Programmable Soft-Start
Remote Output Voltage Sense
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Protection features include: internal foldback current lim-
iting, output overvoltage crowbar and optional short-cir-
cuitshutdown.Soft-startisprovidedbyanexternalcapaci-
tor that can be used to properly sequence supplies. The
operatingcurrentlevelisuser-programmableviaanexter-
nal current sense resistor. Wide input supply range allows
operation from 3.5V to 30V (36V maximum).
Pin defeatable Burst ModeTM operation provides high effi-
ciency at low load currents. OPTI-LOOP compensation
allows the transient response to be optimized over a wide
range of output capacitance and ESR values.
Available in 24-LUead SSOP Package
APPLICATIO S
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Notebook and Palmtop Computers, PDAs
Power Supply for Mobile Pentium® II and
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Pentium III Processors
Low Voltage Power Supplies
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, LTC and LT are registered trademarks of Linear Technology Corporation.
OPTI-LOOP and Burst Mode are trademarks of Linear Technology Corporation.
Pentium is a registered trademark of Intel Corporation.
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TYPICAL APPLICATIO
V
C
IN
OSC
5V TO 24V
47pF
C
V
IN
OSC
C
IN
C
SS
0.1µF
22µF/50V
×2
M1
TG
L1
1.2µH
FDS6680A
R
CERAMIC
SENSE
0.004Ω
RUN/SS
V
OUT
C
C1
330pF
SW
1.35V TO 1.60V
12A
R
C
33k
D
B
LTC1736
VIDV
CMDSH-3
CC
CC
C
B
0.22µF
I
TH
+
C
OUT
C
C2
47pF
INTV
180µF/4V
×4
PGOOD
VID4
BOOST
+
VID3
4.7µF
VID2
M2
FDS6680A
×2
D1
BG
VID1
MBRS340T3
C
: PANASONIC EEFUEOG181R
OUT
VID0
C
: MARCON THCR70EIH226ZT
IN
SGND
PGND
+
L1: PANASONIC ETQP6RZIR20HFA
: IRC LRF2010-01-R004J
–
V
SENSE SENSE
1000pF
OSENSE
R
SENSE
47pF
1736 F01
Figure 1. High Efficiency Step-Down Converter
1