LTC1149_15 Datasheet, PDF (1/20 Pages) Linear Technology – High Efficiency Synchronous Step-Down Switching Regulators

LTC1149
LTC1149-3.3/LTC1149-5
High Efficiency Synchronous
Step-Down Switching Regulators
FEATURES
s _{Operation to 48V Input Voltage}
s _{Ultrahigh Efficiency: Up to 95%}
s _{Current Mode Operation for Excellent Line and}
Load Transient Response
s _{High Efficiency Maintained over Wide Current Range}
s _{Logic-Controlled Micropower Shutdown}
s _{Short-Circuit Protection}
s _{Very Low Dropout Operation: 100% Duty Cycle}
s _{Synchronous FET Switching for High Efficiency}
s _{Adaptive Nonoverlap Gate Drives}
s _{Available in 16-Pin Narrow SO Package}
APPLICATI S
s _{Notebook and Palmtop Computers}
s _{Portable Instruments}
s _{Battery-Operated Digital Devices}
s _{Industrial Power Distribution}
s _{Avionics Systems}
s _{Telecom Power Supplies}
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
DESCRIPTIO
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.
TYPICAL APPLICATI
V_IN
1N4148
+
3.3µF
CAP
0.068µF
V_CC
V_CC
V_IN
PGATE
PDRIVE
LTC1149-5
0V = NORMAL
>2V = SHUTDOWN
3300µF
1k
C_T
470pF
SHDN1
SHDN2
I_TH
C_T
SGND
SENSE ⁺
SENSE ^–
NGATE
P, RGNDS
1N4148
0.047µF
D1
1N5819
+
P-CHANNEL
IRFR9024
C_IN
100µF
100V
L*
62µH
R_SENSE**
0.05Ω
V_OUT
5V/2A
1000pF
N-CHANNEL
IRFR024
+
C_OUT
220µF
*COILTRONICS CTX62-2-MP
**KRL SL-1-C1-0R050J
1149 F01
Figure 1. High Efficiency Step-Down Regulator
LTC1149-5 Efficiency
100
FIGURE 1 CIRCUIT
V_IN = 12V
90
V_IN = 24V
80
70
60
0.02
0.2
LOAD CURRENT (A)
2
1149 TA01
1