LTC1735-1
High Efficiency
Synchronous Step-Down
Switching Regulator
U
FEATURES
DESCRIPTIO
The LTC®1735-1 is a synchronous step-down switching
regulatorcontrolleroptimizedforCPUpower. OPTI-LOOP
compensation allows the transient response to be opti-
mized over a wide range of output capacitance and ESR
values.
■
Dual N-Channel MOSFET Synchronous Drive
■
Programmable/Synchronizable Fixed Frequency
■
VOUT Range: 0.8V to 7V
Wide VIN Range: 3.5V to 36V Operation
■
■
Very Low Dropout Operation: 99% Duty Cycle
OPTI-LOOPTM Compensation Minimizes COUT
■
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.
■
±
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: IQ < 25µA
■
■
■
■
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 ModeTM operation provides high
efficiency at low load currents while 99% duty cycle
provides low dropout operation.
Available in 16-LUead Narrow SSOP and SO Packages
APPLICATIO S
■
Notebook and Palmtop Computers, PDAs
Power Supply for Mobile Pentium® III Processor with
■
SpeedStepTM 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.
U
TYPICAL APPLICATIO
PGOOD
V
IN
4.5V TO 24V
C
C
: MARCON THCR70E1H226ZT
: PANASONIC EEFUE06181R
C
22µF
50V
CERAMIC
×2
IN
OUT
IN
L1: PANASONIC ETQP6RZ1R20HFA
C
47pF
1
2
3
4
5
6
7
8
OSC
16
15
14
13
12
11
10
9
Q1
FDS6680A
C
TG
R
: IRC CRF2010-01-R004J
OSC
SENSE
C
0.22µF
C
0.1µF
B
SS
RUN/SS
BOOST
L1
R
33k
R
C1
SENSE
0.004Ω
C
330pF
C2
1.2µH
V
OUT
I
LTC1735-1 SW
TH
C
C1
47pF
1.35V TO 1.60V
12A
D1
PGOOD
V
IN
CMDSH-3
D2
R1
–
SENSE
SENSE
INTV
CC
MBRS340T3
10k
0.5%
+
47pF
47pF
1000pF
C
OUT
+
Q2, Q3
FDS6680A
×2
47pF
BG
4.7µF
+
180µF
R3
33.2k
1%
4V
V
PGND
OSENSE
PANASONIC SP
5V
(OPTIONAL)
SGND
EXTV
CC
×4
Q4
2N7002
V
V
= 1: V
= 0: V
= 1.60V
= 1.35V
SEL
SEL
OUT
OUT
10Ω
10Ω
R2
14.3k
0.5%
GND
1735-1 F01
Figure 1. CPU Core DC/DC Converter with Dynamic Voltage Selection from SpeedStep Enabled Processors
1