LTC1474/LTC1475
Low Quiescent Current
High Efficiency Step-Down
Converters
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FEATURES
DESCRIPTION
The LTC®1474/LTC1475 series are high efficiency step-
down converters with internal P-channel MOSFET power
switches that draw only 10µA typical DC supply current at
no load while maintaining output voltage. The LTC1474
uses logic-controlled shutdown while the LTC1475 fea-
tures pushbutton on/off.
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High Efficiency: Over 92% Possible
Very Low Standby Current: 10µA Typ
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Available in Space Saving 8-Lead MSOP Package
Internal 1.4Ω Power Switch (VIN = 10V)
Wide VIN Range: 3V to 18V Operation
Very Low Dropout Operation: 100% Duty Cycle
Low-Battery Detector Functional During Shutdown
Programmable Current Limit with Optional
Current Sense Resistor (10mA to 400mA Typ)
Short-Circuit Protection
The low supply current coupled with Burst ModeTM opera-
tion enables the LTC1474/LTC1475 to maintain high effi-
ciency over a wide range of loads. These features, along
with their capability of 100% duty cycle for low dropout
andwideinputsupplyrange, maketheLTC1474/LTC1475
idealformoderatecurrent(upto300mA)battery-powered
applications.
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Few External Components Required
Active Low Micropower Shutdown: IQ = 6µA Typ
Pushbutton On/Off (LTC1475 Only)
3.3V, 5V and Adjustable Output Versions
The peak switch current is user-programmable with an
optionalsenseresistor(defaultsto325mAminimumifnot
used) providing a simple means for optimizing the design
for lower current applications. The peak current control
also provides short-circuit protection and excellent start-
upbehavior.Alow-batterydetectorthatremainsfunctional
in shutdown is provided .
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APPLICATIONS
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Cellular Telephones and Wireless Modems
4mA to 20mA Current Loop Step-Down Converter
Portable Instruments
Battery-Operated Digital Devices
Battery Chargers
Inverting Converters
Intrinsic Safety Applications
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The LTC1474/LTC1475 series availability in 8-lead MSOP
and SO packages and need for few additional components
provide for a minimum area solution.
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, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
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TYPICAL APPLICATION
LTC1474 Efficiency
100
V
IN
LOW BATTERY OUT
4V TO 18V
V
IN
= 5V
+
90
80
70
60
50
10µF
25V
V
IN
= 10V
0.1µF
7
V
IN
1
2
6
3
V
OUT
SENSE
V
V
IN
= 15V
FB
3.3V AT 250mA
LTC1474-3.3
+
L1
100µH
LBI
LBO
SW
LOW BATTERY IN
RUN SHDN
100µF
6.3V
100k
8
5
RUN
GND
4
D1
MBR0530
L = 100µH
V
R
= 3.3V
OUT
SENSE
1474/75 F01
= 0Ω
L1 = SUMIDA CDRH74-101
0.03
0.3
3
30
300
Figure 1. High Efficiency Step-Down Converter
LOAD CURRENT (mA)
1474/75 TA01
1