LT3991/LT3991-3.3/LT3991-5
55V, 1.2A Step-Down
Regulator with 2.8A
Quiescent Current
Fea T Descrip T
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Ultralow Quiescent Current: The LT 3991 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 55V. Low quiescent current design consumes only
2.1A I Regulating 12V 2.8A of supply current while regulating with no load. Low
Q IN
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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 55V 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 0.44 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 LT3991, 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 CapabilityV 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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Saturating Switch Design: 0.44 On-Resistance age. The LT3991 is available in small 10-pin MSOP and
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Output Voltage: 1.19V to 30V 3mm 3mm DFN packages with exposed pads for low
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Small Thermally Enhanced 10-Pin MSOP Package thermal resistance.
and (3mm 3mm) DFN Packages L, LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks
of Linear Technology Corporation. All other trademarks are the property of their respective
owners.
a T
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Automotive Battery Regulation
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Power for Portable Products
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Industrial Supplies
No Load Supply Current
Typical a T
3.0
OUTPUT IN REGULATION
3.3V Step Down Converter
V
IN
4.3V TO 55V
2.5
V
IN
EN./UVLO BOOST
OFF ON
LT3991-5
0.47F
12H
2.0
PG
SW
LT3991-3.3
SS
LT3991-3.3
4.7F
RT
1.5
BD
V
OUT
118k 3.3V
V
OUT
SYNC GND
1.2A
47F
1.0
5 10 15 30 35 40 45 50 55
20 25
3991 TA01a
INPUT VOLTAGE (V)
f = 400kHz
3991 G06
3991fa
1
INPUT CURRENT (A)
ion pplica
ions pplica
ion uresLT3991/LT3991-3.3/LT3991-5
a Te Maxi Mu M r a T
(Note 1)
V , EN Voltage .........................................................55V Operating Junction Temperature Range (Note 2)
IN
BOOST Pin Voltage ...................................................75V LT3991E ............................................. 40C to 125C
BOOST Pin Above SW Pin .........................................30V LT3991I .............................................. 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
p in c F T
LT3991 LT3991 LT3991-3.3, LT3991-5
TOP VIEW
TOP VIEW TOP VIEW
BD 1 10 SYNC
BD 1 10 SYNC BD 1 10 SYNC
BOOST 9 PG
2
BOOST 2 9 PG BOOST 2 9 PG
11 11 11
3 SW 3 8 RT SW 3 8 RT
SW 8 RT
GND GND GND
V 4 7 SS V 4 7 SS
IN IN
V 4 7 SS
IN
EN 5 6 FB EN 5 6 V
OUT
EN 5 6 FB
MSE PACKAGE MSE PACKAGE
10-LEAD PLASTIC MSOP 10-LEAD PLASTIC MSOP
DD PACKAGE
= 45C, = 10C/W = 45C, = 10C/W
JA JC JA JC
10-LEAD (3mm 3mm) PLASTIC DFN
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB 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
o r Der i n F Ma T
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LT3991EDD#PBF LT3991EDD#TRPBF LFJR 40C to 125C
10-Lead (3mm 3mm) Plastic DFN
LT3991IDD#PBF LT3991IDD#TRPBF LFJR 10-Lead (3mm 3mm) Plastic DFN 40C to 125C
LT3991EMSE#PBF LT3991EMSE#TRPBF LTFJS 10-Lead Plastic MSOP 40C to 125C
LT3991IMSE#PBF LT3991IMSE#TRPBF LTFJS 10-Lead Plastic MSOP 40C to 125C
LT3991EMSE-3.3#PBF LT3991EMSE-3.3#TRPBF LTFRS 10-Lead Plastic MSOP 40C to 125C
LT3991IMSE-3.3#PBF LT3991IMSE-3.3#TRPBF LTFRS 10-Lead Plastic MSOP 40C to 125C
LT3991EMSE-5#PBF LT3991EMSE-5#TRPBF LTFRV 10-Lead Plastic MSOP 40C to 125C
LT3991IMSE-5#PBF LT3991IMSE-5#TRPBF LTFRV 10-Lead Plastic MSOP 40C to 125C
Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.
Consult LTC Marketing for information on non-standard lead based finish parts.
For more information on lead free part marking, go to: