FEATURES
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LTC1735-1
High Efficiency
Synchronous Step-Down
Switching Regulator
DESCRIPTIO
The LTC
®
1735-1 is a synchronous step-down switching
regulator controller optimized for CPU power. OPTI-LOOP
compensation allows the transient response to be opti-
mized over a wide range of output capacitance and ESR
values.
The operating frequency (synchronizable up to 500kHz) is
set by an external capacitor allowing maximum flexibility
in optimizing efficiency. The output voltage is monitored
by a power good window comparator that indicates when
the output is within 7.5% of its programmed value, con-
forming to Intel Mobile CPU Specifications.
Protection features include internal foldback current lim-
iting, output overvoltage crowbar and optional short-
circuit shutdown. Soft-start is provided by an external
capacitor that can be used to properly sequence supplies.
The operating current level is user-programmable via an
external current sense resistor. Wide input supply range
allows operation from 3.5V to 30V (36V maximum).
Pin defeatable Burst Mode
TM
operation provides high
efficiency at low load currents while 99% duty cycle
provides low dropout operation.
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Dual N-Channel MOSFET Synchronous Drive
Programmable/Synchronizable Fixed Frequency
V
OUT
Range: 0.8V to 7V
Wide V
IN
Range: 3.5V to 36V Operation
Very Low Dropout Operation: 99% Duty Cycle
OPTI-LOOP
TM
Compensation Minimizes C
OUT
±
1% Output Voltage Accuracy
Power Good Output Voltage Monitor
Internal Current Foldback
Output Overvoltage Crowbar Protection
Latched Short-Circuit Shutdown Timer
with Defeat Option
Optional Programmable Soft-Start
Remote Output Voltage Sense
Logic Controlled Micropower Shutdown: I
Q
< 25µA
Available in 16-Lead Narrow SSOP and SO Packages
APPLICATIO S
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Notebook and Palmtop Computers, PDAs
Power Supply for Mobile Pentium
®
III Processor with
SpeedStep
TM
Technology
Cellular Telephones and Wireless Modems
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode and OPTI-LOOP are trademarks of Linear Technology Corporation.
Pentium is a registered trademark of Intel Corporation. SpeedStep is a trademark of Intel
Corporation.
TYPICAL APPLICATIO
PGOOD
C
OSC
47pF
C
SS
0.1µF
C
C2
330pF
R
C1
33k
C
C1
47pF
1
2
3
4
5
47pF
1000pF 6
7
8
V
IN
4.5V TO 24V
C
OSC
RUN/SS
I
TH
TG
BOOST
SW
V
IN
INTV
CC
BG
PGND
EXTV
CC
10Ω
10Ω
16
15
14
13
12
11
10
9
5V
(OPTIONAL)
D1
CMDSH-3
C
B
0.22µF
Q1
FDS6680A
L1
1.2µH
D2
MBRS340T3
Q2, Q3
FDS6680A
×2
C
IN
22µF
50V
CERAMIC
×2
R
SENSE
0.004Ω
LTC1735-1
–
PGOOD
SENSE
SENSE
+
V
OSENSE
SGND
+
4.7µF
Figure 1. CPU Core DC/DC Converter with Dynamic Voltage Selection from SpeedStep Enabled Processors
U
U
U
C
IN
: MARCON THCR70E1H226ZT
C
OUT
: PANASONIC EEFUE06181R
L1: PANASONIC ETQP6RZ1R20HFA
R
SENSE
: IRC CRF2010-01-R004J
V
OUT
1.35V TO 1.60V
12A
C
OUT
180µF
4V
PANASONIC SP
×4
V
SEL
= 1: V
OUT
= 1.60V
V
SEL
= 0: V
OUT
= 1.35V
GND
1735-1 F01
47pF
R1
10k
0.5%
+
47pF
R2
14.3k
0.5%
R3
33.2k
1%
Q4
2N7002
1
LINER [ LINEAR TECHNOLOGY ]
