LT3973/LT3973-3.3/LT3973-5
42V, 750mA Step-Down
Regulator with 2.5µA
Quiescent Current and
Integrated Diodes
FEATURES
DESCRIPTION
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Ultralow Quiescent Current
The LT®3973 is an adjustable frequency monolithic buck
switchingregulatorthatacceptsawideinputvoltagerange
up to 42V, and consumes only 2.5µA of quiescent current.
A high efficiency switch is included on the die along with
the catch diode, boost diode, and the necessary oscillator,
controlandlogiccircuitry.LowrippleBurstModeoperation
maintainshighefficiencyatlowoutputcurrentswhilekeep-
ing the output ripple below 10mV in a typical application.
Aminimumdropoutvoltageof530mVismaintainedwhen
theinputvoltagedropsbelowtheprogrammedoutputvolt-
age, such as during automotive cold crank. Current mode
topologyisusedforfasttransientresponseandgoodloop
stability. A catch diode current limit provides protection
against shorted outputs and overvoltage conditions, with
thermalshutdownprovidingadditionalfaultprotection.An
accurate programmable undervoltage lockout feature is
available, producing a low shutdown current of 0.75µA.
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2.5µA I at 12V to 3.3V
Q
IN
OUT
Low Ripple Burst Mode® Operation
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Output Ripple < 10mV
P-P
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Wide Input Voltage Range: 4.2V to 42V Operating
Adjustable Switching Frequency: 200kHz to 2.2MHz
Integrated Boost and Catch Diodes
750mA Output Current
Excellent Start-Up and Dropout Performance
Fixed Output Voltages: 3.3V, 5V
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1.9µA I at 12V
Q
IN
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Accurate Programmable Undervoltage Lockout
Low Shutdown Current: I = 0.75µA
Internal Catch Diode Current Limit
Power Good Flag
Thermal Shutdown
Small, Thermally Enhanced 10-Lead MSOP and
(3mm × 3mm) DFN Packages
Q
A power good flag signals when V
reaches 90% of
OUT
the programmed output voltage. The LT3973 is available
in small, thermally enhanced 10-lead MSOP and 3mm ×
3mm DFN packages.
APPLICATIONS
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Automotive Battery Regulation
Power for Portable Products
Industrial Supplies
Gate Drive Bias
L, LT, LTC, LTM, Linear Technology, the Linear logo and Burst Mode are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
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Efficiency
TYPICAL APPLICATION
90
80
70
60
50
40
1000
100
10
V
= 12V
IN
5V Step-Down Converter
V
IN
5.6V TO 42V
C3
0.47µF
V
BOOST
LT3973
EN/UVLO SW
IN
L1
15µH
V
OUT
5V
OFF ON
1
750mA
PG
BD
OUT
FB
15pF
1M
C1
C2
22µF
RT
0.1
0.01
4.7µF
GND
215k
f = 600kHz
316k
3973 TA01a
0.01
0.1
1
10
100
LOAD CURRENT (mA)
3973 TA01b
3973fb
1
For more information www.linear.com/LT3973