LTC1474_15 Datasheet, PDF (1/20 Pages) Linear Technology – Low Quiescent Current High Efficiency Step-Down Converters

FEATURES
s _{High Efficiency: Over 92% Possible}
s _{Very Low Standby Current: 10µA Typ}
s _{Available in Space Saving 8-Lead MSOP Package}
s _{Internal 1.4Ω Power Switch (VIN = 10V)}
s _{Wide VIN Range: 3V to 18V Operation}
s _{Very Low Dropout Operation: 100% Duty Cycle}
s _{Low-Battery Detector Functional During Shutdown}
s _{Programmable Current Limit with Optional}
Current Sense Resistor (10mA to 400mA Typ)
s _{Short-Circuit Protection}
s _{Few External Components Required}
s _{Active Low Micropower Shutdown: IQ = 6µA Typ}
s _{Pushbutton On/Off (LTC1475 Only)}
s _{3.3V, 5V and Adjustable Output Versions}
U
APPLICATIONS
s _{Cellular Telephones and Wireless Modems}
s _{4mA to 20mA Current Loop Step-Down Converter}
s _{Portable Instruments}
s _{Battery-Operated Digital Devices}
s _{Battery Chargers}
s _{Inverting Converters}
s _{Intrinsic Safety Applications}
LTC1474/LTC1475
Low Quiescent Current
High Efficiency Step-Down
Converters
DESCRIPTION
The LT C^®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.
The low supply current coupled with Burst Mode^TM 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
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 start-
up behavior. A low-battery detector that remains functional
in shutdown is provided .
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.
TYPICAL APPLICATION
V_IN
4V TO 18V
+ _10µF
25V
0.1µF
LOW BATTERY IN
7
6
V_IN
SENSE
1
V_FB
3
LBI
LTC1474-3.3
LBO
2
RUN SHDN
100k ₈
RUN
GND
4
5
SW
L1 = SUMIDA CDRH74-101
LOW BATTERY OUT
L1
+
100µH
V_OUT
3.3V AT 250mA
100µF
6.3V
D1
MBR0530
1474/75 F01
Figure 1. High Efficiency Step-Down Converter
LTC1474 Efficiency
100
90
V_IN = 5V
V_IN = 10V
80
V_IN = 15V
70
60
50
0.03
L = 100µH
V_OUT = 3.3V
R_SENSE = 0Ω
0.3
3
30
300
LOAD CURRENT (mA)
1474/75 TA01
1