LTC1474/LTC1475
Low Quiescent Current
High Efficiency Step-Down
Converters
DESCRIPTION
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FEATURES
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The LT C®1474/LTC1475 series are high efficiency stepdown 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 features pushbutton on/off.
High Efficiency: Over 92% Possible
Very Low Standby Current: 10µA Typ
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
Few External Components Required
Active Low Micropower Shutdown: IQ = 6µA Typ
Pushbutton On/Off (LTC1475 Only)
3.3V, 5V and Adjustable Output Versions
The low supply current coupled with Burst ModeTM operation enables the LTC1474/LTC1475 to maintain high efficiency over a wide range of loads. These features, along
with their capability of 100% duty cycle for low dropout
and wide input supply range, make the LTC1474/LTC1475
ideal for moderate current (up to 300mA) battery-powered
applications.
The peak switch current is user-programmable with an
optional sense resistor (defaults to 325mA minimum if not
used) providing a simple means for optimizing the design
for lower current applications. The peak current control
also provides short-circuit protection and excellent startup behavior. A low-battery detector that remains functional
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
The LTC1474/LTC1475 series availability in 8-lead MSOP
and SO packages and need for few additional components
provide for a minimum area solution.
, 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
VIN
4V TO 18V
LOW BATTERY OUT
VIN = 5V
90
10µF
25V
0.1µF
VIN = 10V
7
VIN
1
SENSE
VFB
LTC1474-3.3
3
2
LBO
LBI
6
LOW BATTERY IN
RUN SHDN
100k
8
RUN
GND
4
SW
VOUT
3.3V AT 250mA
L1
100µH
+
100µF
6.3V
5
D1
MBR0530
EFFICIENCY (%)
+
80
VIN = 15V
70
60
L = 100µH
VOUT = 3.3V
RSENSE = 0Ω
1474/75 F01
L1 = SUMIDA CDRH74-101
50
Figure 1. High Efficiency Step-Down Converter
0.03
3
0.3
30
LOAD CURRENT (mA)
300
1474/75 TA01
1