LT1939EDD Datasheet, PDF (1/24 Pages) Linear Technology – Monolithic 2A Step-Down Regulator Plus Linear Regulator/Controller

FEATURES
n _{Wide Input Range: 3V to 25V}
n _{Short-Circuit Protected Over Full Input Range}
n _{2A Output Current Capability}
n _{Adjustable/Synchronizable Fixed Frequency}
Operation from 250kHz to 2.2MHz
n _{Soft-Start/Tracking Capability}
n _{Output Adjustable Down to 0.8V}
n _{Adjustable Linear Regulator/Driver with 13mA}
Output Capability
n _{Power Good Comparator with Complementary}
Outputs
n _{Low Shutdown Current: 12μA}
n _{Thermally Enhanced 3mm × 3mm DFN Package}
APPLICATIONS
n _{Automotive Battery Regulation}
n _{Industrial Control}
n _{Wall Transformer Regulation}
n _{Distributed Power Regulation}
LT1939
Monolithic 2A Step-Down
Regulator Plus Linear
Regulator/Controller
DESCRIPTION
The LT^®1939 is a current mode PWM step-down DC/DC
converter with an internal 2.3A switch. The wide input
range of 3V to 25V makes the LT1939 suitable for regu-
lating power from a wide variety of sources, including
automotive batteries, industrial supplies and unregulated
wall adapters.
Resistor-programmable 250kHz to 2.2MHz frequency
range and synchronization capability enable optimization
between efficiency and external component size. Cycle-
by-cycle current limit, frequency foldback and thermal
shutdown provide protection against a shorted output.
The soft-start feature controls the ramp rate of the output
voltage, eliminating input current surge during start-up,
and also provides output tracking.
The LT1939 contains an internal NPN transistor with feed-
back control which can be configured as a linear regulator
or as a linear regulator controller.
The LT1939’s low current shutdown mode (<12μA) enables
easy power management in battery-powered systems.
L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
Dual Step-Down Converters
V_IN
6V TO 25V
2.2μF
0.47μF
V_IN
BST
LT1939
SW
SHDN
SS
FB
PG
PG
BAT54
0.47μF
6.8μH
B240A
42.2k
8.06k
V_OUT1
5V
1A
22μF
53.6k
330pF
40.2k
R_T/SYNC LDRV
V_C
LFB
1k
24.9k
8.06k
V_OUT2
3.3V
22μF ^1A
1939 TA01a
Switching Converter Efficiency
90
85
80
V_OUT1 = 5V AT 1A
AC COUPLED
75
2mV/DIV
70
65
60
55
V_IN = 12V
I_OUT2 = 0A
FREQUENCY = 800kHz
50
0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0
LOAD CURRENT (A)
1939 TA01b
V_OUT2 = 3.3V AT 1A
AC COUPLED
2mV/DIV
Output Voltage Ripple
500ns/DIV
1939 TA01c
1939f
1