LT3971/LT3971-3.3/LT3971-5
38V, 1.2A, 2MHz
Step-Down Regulator with
2.8A Quiescent Current
FEATURES DESCRIPTION
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Ultralow Quiescent Current: The LT 3971 is an adjustable frequency monolithic buck
2.8A I Regulating 12V to 3.3V switching regulator that accepts a wide input voltage range
Q IN OUT
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Fixed Output Voltages: 3.3V, 5V, up to 38V. Low quiescent current design consumes only
2.1A I Regulating 12V to 3.3V 2.8A of supply current while regulating with no load. Low
Q IN OUT
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Low Ripple Burst Mode Operation: ripple Burst Mode operation maintains high efficiency at
Output Ripple < 15mV low output currents while keeping the output ripple below
P-P
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Wide Input Voltage Range: 4.3V to 38V 15mV in a typical application. An internally compensated
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1.2A Maximum Output Current current mode topology is used for fast transient response
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Adjustable Switching Frequency: 200kHz to 2MHz and good loop stability. A high efficiency 0.33 switch
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Synchronizable Between 250kHz to 2MHz is included on the die along with a boost Schottky diode
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Fast Transient Response and the necessary oscillator, control and logic circuitry.
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Accurate 1V Enable Pin Threshold An accurate 1V threshold enable pin can be used to shut
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Low Shutdown Current: I = 700nA down the LT3971, reducing the input supply current to
Q
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Power Good Flag 700nA. A capacitor on the SS pin provides a controlled
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Soft-Start Capability inrush current (soft-start). A power good flag signals
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Internal Compensation when V reaches 91% of the programmed output volt-
OUT
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Output Voltage: 1.19V to 30V age. The LT3971 is available in small 10-lead MSOP and
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Small Thermally Enhanced 10-Lead MSOP, 16-Lead 3mm 3mm DFN packages with exposed pads for low
MSOP and (3mm 3mm) DFN Packages thermal resistance. A 16-lead MSOP is also offered which
has enhanced pin-to-pin fault tolerance.
APPLICATIONS 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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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
OFF ON 2.5
LT3971-5
0.47F
4.7H
PG
SW
SS
4.7F 2.0
LT3971-3.3
LT3971-3.3
RT
BD
V
OUT
1.5
3.3V
V
49.9k OUT
SYNC GND
1.2A
22F
f = 800kHz
1.0
3971 TA01
5 10 15 20 25 30 35
INPUT VOLTAGE (V)
3971 TA01b
3971fd
1
INPUT CURRENT (A)LT3971/LT3971-3.3/LT3971-5
ABSOLUTE MAXIMUM RATINGS (Note 1)
V , EN Voltage .........................................................38V Operating Junction Temperature Range (Note 2)
IN
BOOST Pin Voltage ...................................................55V LT3971E ............................................. 40C to 125C
BOOST Pin Above SW Pin .........................................30V LT3971I .............................................. 40C to 125C
FB, V , RT, SYNC, SS Voltage .................................6V Storage Temperature Range .............. 65C to 150C
OUT
PG, BD Voltage .........................................................30V Lead Temperature (Soldering, 10 sec)
Boost Diode Current ....................................................1A (MSE Only) .......................................................300C
PIN CONFIGURATION
LT3971 LT3971 LT3971
TOP VIEW
TOP VIEW
TOP VIEW
1
BD 16 GND
BD 1 10 SYNC
NC 2 15 SYNC
BD 1 10 SYNC
3
BOOST 2 9 PG BOOST 14 PG
BOOST 2 9 PG
11 11
NC 4 17 13 RT
SW 3 8 RT
SW 3 8 RT
GND GND 5
SW GND 12 SS
V 4 7 SS
IN
V 4 7 SS NC 6 11 NC
IN
EN 5 6 FB
7
V 10 FB
IN
EN 5 6 FB
EN 8 9 FB
MSE PACKAGE
10-LEAD PLASTIC MSOP
MSE PACKAGE
DD PACKAGE
= 45C, = 10C/W
16-LEAD PLASTIC MSOP
JA JC
10-LEAD (3mm 3mm) PLASTIC DFN
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
= 40C
JA
= 45C, = 10C/W
JA JC
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
LT3971-3.3, LT3971-5 LT3971-3.3, LT3971-5
TOP VIEW
TOP VIEW
BD 1 10 SYNC
BD 1 10 SYNC
BOOST 2 9 PG
BOOST 2 9 PG
11 11
SW 3 8 RT
SW 3 8 RT
GND GND
V 4 7 SS
IN
V 4 7 SS
IN
EN 5 6 V
OUT
EN 5 6 V
OUT
MSE PACKAGE
10-LEAD PLASTIC MSOP
DD PACKAGE
= 45C, = 10C/W
JA JC
10-LEAD (3mm 3mm) PLASTIC DFN
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
= 45C, = 10C/W
JA JC
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LT3971EDD#PBF LT3971EDD#TRPBF LFJF 10-Lead (3mm 3mm) Plastic DFN 40C to 125C
LT3971IDD#PBF LT3971IDD#TRPBF LFJF 10-Lead (3mm 3mm) Plastic DFN 40C to 125C
LT3971EMSE#PBF LT3971EMSE#TRPBF LTFJG 10-Lead Plastic MSOP 40C to 125C
LT3971IMSE#PBF LT3971IMSE#TRPBF LTFJG 10-Lead Plastic MSOP 40C to 125C
LT3971EMSE16#PBF LT3971EMSE16#TRPBF 3971 16-Lead Plastic MSOP 40C to 125C
LT3971IMSE16#PBF LT3971IMSE16#TRPBF 3971 16-Lead Plastic MSOP 40C to 125C
LT3971EDD-3.3#PBF LT3971EDD-3.3#TRPBF LFRM 40C to 125C
10-Lead (3mm 3mm) Plastic DFN
LT3971IDD-3.3#PBF LT3971IDD-3.3#TRPBF LFRM 10-Lead (3mm 3mm) Plastic DFN 40C to 125C
LT3971EMSE-3.3#PBF LT3971EMSE-3.3#TRPBF LTFRN 10-Lead Plastic MSOP 40C to 125C
LT3971IMSE-3.3#PBF LT3971IMSE-3.3#TRPBF LTFRN 10-Lead Plastic MSOP 40C to 125C
3971fd
2