1
LTC1474/LTC1475
Low Quiescent Current
High Efficiency Step-Down
Converters
LOAD CURRENT (mA)
EFFICIENCY (%)
100
90
80
70
60
50
0.03 3 300
1474/75 TA01
0.3 30
V
IN
= 5V
V
IN
= 10V
V
IN
= 15V
L = 100µH
V
OUT
= 3.3V
R
SENSE
= 0Ω
LTC1474 Efficiency
Figure 1. High Efficiency Step-Down Converter
V
IN
GND
SENSE
LBI
RUN
V
FB
LBO
SW
LTC1474-3.3
+
6
3
8
1
2
5
7
4
100k
LOW BATTERY IN
RUN SHDN
0.1µF
10µF
25V
V
IN
4V TO 18V
LOW BATTERY OUT
1474/75 F01
L1
100µH
D1
MBR0530
+
100µF
6.3V
V
OUT
3.3V AT 250mA
L1 = SUMIDA CDRH74-101
FEATURES
DESCRIPTION
U
■
High Efficiency: Over 92% Possible
■
Very Low Standby Current: 10
µ
A Typ
■
Available in Space Saving 8-Lead MSOP Package
■
Internal 1.4Ω Power Switch (V
IN
= 10V)
■
Wide V
IN
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: I
Q
= 6µA Typ
■
Pushbutton On/Off (LTC1475 Only)
■
3.3V, 5V and Adjustable Output Versions
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.
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.
APPLICATIONS
U
■
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
TYPICAL APPLICATION
U
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
