Datasheet
1
LTC1149
LTC1149-3.3/LTC1149-5
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ESCRIPTIO
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Operation to 48V Input Voltage
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Ultrahigh Efficiency: Up to 95%
■
Current Mode Operation for Excellent Line and
Load Transient Response
■
High Efficiency Maintained over Wide Current Range
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Logic-Controlled Micropower Shutdown
■
Short-Circuit Protection
■
Very Low Dropout Operation: 100% Duty Cycle
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Synchronous FET Switching for High Efficiency
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Adaptive Nonoverlap Gate Drives
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Available in 16-Pin Narrow SO Package
The LTC
®
1149 series is a family of synchronous step-
down switching regulator controllers featuring automatic
Burst Mode
TM
operation to maintain high efficiencies at
low output currents. These devices drive external comple-
mentary power MOSFETs at switching frequencies up
to 250kHz using a constant off-time current-mode archi-
tecture.
Special onboard regulation and level-shift circuitry allow
operation at input voltages from dropout to 48V (60V
absolute max). The constant off-time architecture main-
tains constant ripple current in the inductor, easing the
design of wide input range converters. Current mode
operation provides excellent line and load transient
response. The operating current level is user-program-
mable via an external current sense resistor.
The LTC1149 series incorporates automatic power saving
Burst Mode
operation when load currents drop below the
level required for continuous operation. Standby power is
reduced to only about 8mW at V
IN
= 12V. In shutdown,
both MOSFETs are turned off.
High Efficiency Synchronous
Step-Down Switching Regulators
Figure 1. High Efficiency Step-Down Regulator
U
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L
IC
AT
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P
I
CA
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0.068µF
V
IN
CAP
PDRIVE
LTC1149-5
SHDN1
I
TH
C
T
SGND
PGATE
V
CC
V
CC
SHDN2
SENSE
–
SENSE
+
P, RGNDS
NGATE
1000pF
N-CHANNEL
IRFR024
0.047µF
1N4148
1N4148
V
IN
P-CHANNEL
IRFR9024
D1
1N5819
L*
62µH
R
SENSE
**
0.05Ω
V
OUT
5V/2A
C
OUT
220µF
C
IN
100µF
100V
3.3µF
0V = NORMAL
>2V = SHUTDOWN
3300µF
C
T
470pF
1k
1149 F01
*COILTRONICS CTX62-2-MP
**KRL SL-1-C1-0R050J
+
+
+
LOAD CURRENT (A)
0.02
60
EFFICIENCY (%)
70
80
100
0.2 2
1149 TA01
90
V
IN
= 12V
V
IN
= 24V
FIGURE 1 CIRCUIT
LTC1149-5 Efficiency
■
Notebook and Palmtop Computers
■
Portable Instruments
■
Battery-Operated Digital Devices
■
Industrial Power Distribution
■
Avionics Systems
■
Telecom Power Supplies
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AT
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, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode
is a trademark of Linear Technology Corporation.