LT3971/LT3971-3.3/LT3971-5
38V, 1.2A, 2MHz
Step-Down Regulator with
2.8µA Quiescent Current
FEATURES
DESCRIPTION
The LT®3971 is an adjustable frequency monolithic buck
switchingregulatorthatacceptsawideinputvoltagerange
up to 38V. Low quiescent current design consumes only
2.8µAofsupplycurrentwhileregulatingwithnoload. Low
ripple Burst Mode operation maintains high efficiency at
low output currents while keeping the output ripple below
15mV in a typical application. An internally compensated
current mode topology is used for fast transient response
and good loop stability. A high efficiency 0.33Ω switch
is included on the die along with a boost Schottky diode
and the necessary oscillator, control and logic circuitry.
An accurate 1V threshold enable pin can be used to shut
down the LT3971, reducing the input supply current to
700nA. A capacitor on the SS pin provides a controlled
inrush current (soft-start). A power good flag signals
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Ultralow Quiescent Current:
2.8µA I Regulating 12V to 3.3V
Q
IN
OUT
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Fixed Output Voltages: 3.3V, 5V,
2.1µA I Regulating 12V to 3.3V
Q
IN
OUT
Low Ripple Burst Mode® Operation:
Output Ripple < 15mV
P-P
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Wide Input Voltage Range: 4.3V to 38V
1.2A Maximum Output Current
Adjustable Switching Frequency: 200kHz to 2MHz
Synchronizable Between 250kHz to 2MHz
Fast Transient Response
Accurate 1V Enable Pin Threshold
Low Shutdown Current: I = 700nA
Q
Power Good Flag
Soft-Start Capability
Internal Compensation
when V
reaches 91% of the programmed output volt-
OUT
Output Voltage: 1.19V to 30V
Small Thermally Enhanced 10-Lead MSOP, 16-Lead
MSOP and (3mm × 3mm) DFN Packages
age. The LT3971 is available in small 10-lead MSOP and
3mm × 3mm DFN packages with exposed pads for low
thermal resistance. A 16-lead MSOP is also offered which
has enhanced pin-to-pin fault tolerance.
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.
APPLICATIONS
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Automotive Battery Regulation
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Power for Portable Products
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Industrial Supplies
TYPICAL APPLICATION
No Load Supply Current
3.3V Step Down Converter
3.0
OUTPUT IN REGULATION
V
IN
4.5V TO 38V
V
IN
EN
BOOST
SW
2.5
OFF ON
4.7µF
LT3971-5
0.47µF
4.7µH
PG
SS
2.0
LT3971-3.3
LT3971-3.3
RT
BD
V
3.3V
1.2A
OUT
1.5
1.0
V
49.9k
f = 800kHz
OUT
SYNC GND
22µF
3971 TA01
5
10
15
20
25
30
35
INPUT VOLTAGE (V)
3971 TA01b
3971fd
1