LTC1147-3.3
LTC1147-5/LTC1147L
High Efficiency Step-Down
Switching Regulator Controllers
FEATURES
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DESCRIPTIO
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Very High Efficiency: Over 95% Possible
Wide V
IN
Range: 3.5V* to 16V
Current Mode Operation for Excellent Line and Load
Transient Response
High Efficiency Maintained Over Three Decades of
Output Current
Low 160µA Standby Current at Light Loads
Logic Controlled Micropower Shutdown: I
Q
< 20µA
Short-Circuit Protection
Very Low Dropout Operation: 100% Duty Cycle
High Efficiency in a Small Amount of Board Space
Output Can Be Externally Held High in Shutdown
Available in 8-Pin SO Package
The LTC
®
1147 series are step-down switching regulator
controllers featuring automatic Burst Mode
TM
operation to
maintain high efficiencies at low output currents. These
devices drive an external P-channel power MOSFET at
switching frequencies exceeding 400kHz using a constant
off-time current mode architecture providing constant
ripple current in the inductor.
The operating current level is user-programmable via an
external current sense resistor. Wide input supply range
allows operation from 3.5V* to 14V (16V maximum).
Constant off-time architecture provides low dropout regu-
lation limited by only the R
DS(ON)
of the external MOSFET
and resistance of the inductor and current sense resistor.
The LTC1147 series incorporates automatic power saving
Burst Mode operation to reduce switching losses when
load currents drop below the level required for continuous
operation. Standby power is reduced to only 2mW at
V
IN
= 10V (at I
OUT
= 0). Load currents in Burst Mode
operation are typically 0mA to 300mA.
For applications where even higher efficiency is required,
refer to the LTC1148 data sheet and Application Note 54.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
*LTC1147L and LTC1147L-3.3 only.
APPLICATIO S
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Notebook and Palmtop Computers
Portable Instruments
Battery-Operated Digital Devices
Cellular Telephones
DC Power Distribution Systems
GPS Systems
TYPICAL APPLICATI
+
1µF
V
IN
V
IN
(5.2V TO 14V)
+
PDRIVE
LTC1147-5
SHDN
SENSE
+
I
TH
SENSE
–
C
T
GND
P-CHANNEL
Si4431DY
L*
50µH
100
C
IN
100µF
R
SENSE
**
0.05Ω
0V = NORMAL
>1.5V = SHUTDOWN
V
OUT
5V/2A
EFFICIENCY (%)
1000pF
R
C
1k
C
C
3300pF
+
D1
MBRD330
C
T
470pF
C
OUT
390µF
LT1147 • F01
*COILTRONICS CTX50-2-MP
**KRL SL-1-C1-0R050J
Figure 1. High Efficiency Step-Down Converter
sn1147 1147fds
U
LTC1147-5 Efficiency
95
90
V
IN
= 10V
85
80
75
70
0.001
V
IN
= 6V
0.01
0.1
1
LT1147 • TA01
UO
U
LOAD CURRENT (A)
1
LINEAR [ LINEAR INTEGRATED SYSTEMS ]
