LT3991 Datasheet PDF - Linear Technology

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LT3991
Linear Technology

Part Number LT3991
Description 1.2A Step-Down Regulator
Page 24 Pages


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Features
n Ultralow Quiescent Current:
2.8µA IQ Regulating 12VIN to 3.3VOUT
n Fixed Output Voltages: 3.3V, 5V
2.1µA IQ Regulating 12VIN
n Low Ripple Burst Mode® Operation:
Output Ripple < 15mVP-P
n Wide Input Voltage Range: 4.3V to 55V
n 1.2A Maximum Output Current
n Adjustable Switching Frequency: 200kHz to 2MHz
n Synchronizable Between 250kHz to 2MHz
n Fast Transient Response
n Accurate 1V Enable Pin Threshold
n Low Shutdown Current: IQ = 700nA
n Power Good Flag
n Soft-Start CapabilityV
n Internal Compensation
n Saturating Switch Design: 0.44Ω On-Resistance
n Output Voltage: 1.19V to 30V
n Small Thermally Enhanced 10-Pin MSOP Package
and (3mm × 3mm) DFN Packages
Applications
n Automotive Battery Regulation
n Power for Portable Products
n Industrial Supplies
LT3991/LT3991-3.3/LT3991-5
55V, 1.2A Step-Down
Regulator with 2.8µA
Quiescent Current
Description
The LT®3991 is an adjustable frequency monolithic buck
switching regulator that accepts a wide input voltage range
up to 55V. Low quiescent current design consumes only
2.8µA of supply current while regulating with no load. 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 0.44Ω 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 LT3991, 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
when VOUT reaches 91% of the programmed output volt-
age. The LT3991 is available in small 10-pin MSOP and
3mm × 3mm DFN packages with exposed pads for low
thermal resistance.
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.
Typical Application
VIN
4.3V TO 55V
3.3V Step Down Converter
OFF ON
VIN
EN./UVLO
BOOST
4.7µF
PG
SS LT3991-3.3 SW
118k
RT
SYNC
BD
GND VOUT
0.47µF 12µH
47µF
f = 400kHz
3991 TA01a
VOUT
3.3V
1.2A
No Load Supply Current
3.0
OUTPUT IN REGULATION
2.5
LT3991-5
2.0
LT3991-3.3
1.5
1.0
5
10 15 20 25 30 35 40 45 50 55
INPUT VOLTAGE (V)
3991 G06
3991fa
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LT3991/LT3991-3.3/LT3991-5
Absolute Maximum Ratings
(Note 1)
VIN, EN Voltage..........................................................55V
BOOST Pin Voltage....................................................75V
BOOST Pin Above SW Pin..........................................30V
FB, VOUT, RT, SYNC, SS Voltage..................................6V
PG, BD Voltage..........................................................30V
Boost Diode Current.....................................................1A
Operating Junction Temperature Range (Note 2)
LT3991E.............................................. –40°C to 125°C
LT3991I............................................... –40°C to 125°C
Storage Temperature Range............... –65°C to 150°C
Lead Temperature (Soldering, 10 sec)
(MSE Only)........................................................ 300°C
Pin Configuration
LT3991
LT3991
LT3991-3.3, LT3991-5
TOP VIEW
BD
BOOST
SW
VIN
EN
1
2
3
4
5
10 SYNC
9 PG
11
GND
8 RT
7 SS
6 FB
DD PACKAGE
10-LEAD (3mm × 3mm) PLASTIC DFN
θJA = 45°C, θJC = 10°C/W
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
BD 1
BOOST 2
SW 3
VIN 4
EN 5
TOP VIEW
11
GND
10 SYNC
9 PG
8 RT
7 SS
6 FB
MSE PACKAGE
10-LEAD PLASTIC MSOP
θJA = 45°C, θJC = 10°C/W
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
TOP VIEW
BD 1
10 SYNC
BOOST 2
SW 3
VIN 4
11
GND
9 PG
8 RT
7 SS
EN 5
6 VOUT
MSE PACKAGE
10-LEAD PLASTIC MSOP
θJA = 45°C, θJC = 10°C/W
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
LT3991EDD#PBF
LT3991EDD#TRPBF
LFJR
10-Lead (3mm × 3mm) Plastic DFN
–40°C to 125°C
LT3991IDD#PBF
LT3991IDD#TRPBF
LFJR
10-Lead (3mm × 3mm) Plastic DFN
–40°C to 125°C
LT3991EMSE#PBF
LT3991EMSE#TRPBF
LTFJS
10-Lead Plastic MSOP
–40°C to 125°C
LT3991IMSE#PBF
LT3991IMSE#TRPBF
LTFJS
10-Lead Plastic MSOP
–40°C to 125°C
LT3991EMSE-3.3#PBF
LT3991EMSE-3.3#TRPBF LTFRS
10-Lead Plastic MSOP
–40°C to 125°C
LT3991IMSE-3.3#PBF
LT3991IMSE-3.3#TRPBF LTFRS
10-Lead Plastic MSOP
–40°C to 125°C
LT3991EMSE-5#PBF
LT3991EMSE-5#TRPBF LTFRV
10-Lead Plastic MSOP
–40°C to 125°C
LT3991IMSE-5#PBF
LT3991IMSE-5#TRPBF LTFRV
10-Lead Plastic MSOP
–40°C to 125°C
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: http://www.linear.com/leadfree/
For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/
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LT3991/LT3991-3.3/LT3991-5
E lectrical Characteristics The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 12V, VEN = 12V, VBD = 3.3V unless otherwise noted. (Note 2)
PARAMETER
Minimum Input Voltage
Quiescent Current from VIN
LT3991 FB Pin Current
Internal Feedback Resistor Divider
Feedback Voltage
LT3991-3.3 Output Voltage
LT3991-5 Output Voltage
FB Voltage Line Regulation
Switching Frequency
Minimum Switch On Time
Minimum Switch Off Time
Switch Current Limit
Switch VCESAT
Switch Leakage Current
Boost Schottky Forward Voltage
Boost Schottky Reverse Leakage
Minimum Boost Voltage (Note 3)
BOOST Pin Current
EN Voltage Threshold
EN Voltage Hysteresis
EN Pin Current
LT3991 PG Threshold Offset from VFB
LT3991 PG Hysteresis
LT3991-X PG Threshold Offset from VOUT
LT3991X PG Hysteresis
PG Leakage
PG Sink Current
SYNC Threshold
SYNC Pin Current
SS Source Current
CONDITIONS
(Note 4)
VEN Low
VVEENN
High,
High,
VVSSYYNNCC
Low
Low
VFB = 1.19V
4.3V < VIN < 40V (Note 4)
RT = 11k
RRTT
=
=
35.7k
255k
ISW = 1A
ISH = 100mA
VREVERSE = 12V
VIN = 5V
ISW = 1A, VBOOST = 15V
EN Rising
VFB Rising
VOUT Rising
VPG = 3V
VPG = 0.4V
VSS = 1V
MIN
l
l
l
1.175
l 1.165
3.25
l 3.224
4.93
l 4.89
1.6
0.8
160
1.7
l
l 0.95
60
5.5
l 300
0.6
0.6
TYP
4
0.7
1.7
0.1
10
1.19
1.19
3.3
3.3
5
5
0.0002
2
1
200
110
150
2.3
440
0.02
800
0.02
1.4
25
1.01
30
0.2
100
20
9
1.3
0.02
570
0.8
0.1
1
MAX
4.3
1.2
2.7
4.5
12
1.205
1.215
3.35
3.376
5.07
5.11
0.01
2.4
1.2
240
200
2.9
1
1
1.8
33
1.07
20
140
12.5
1
1.0
1.6
UNITS
V
μA
μA
μA
nA
V
V
V
V
V
V
%/V
MHz
MHz
kHz
ns
ns
A
mV
μA
mV
μA
V
mA
V
mV
nA
mV
mV
%
%
µA
μA
V
nA
μA
Note 1: Stresses beyond those listed under Absolute Maximum Ratings
may cause permanent damage to the device. Exposure to any Absolute
Maximum Rating condition for extended periods may affect device
reliability and lifetime.
Note 2: The LT3991E is guaranteed to meet performance specifications
from 0°C to 125°C junction temperature. Specifications over the –40°C
to 125°C operating junction temperature range are assured by design,
characterization, and correlation with statistical process controls.
The LT3991I is guaranteed over the full –40°C to 125°C operating junction
temperature range. High junction temperatures degrade operating
lifetimes. Operating lifetime is derated at junction temperatures greater
than 125°C.
Note 3: This is the minimum voltage across the boost capacitor needed to
guarantee full saturation of the switch.
Note 4: Minimum input voltage depends on application circuit.
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LT3991/LT3991-3.3/LT3991-5
Typical Performance Characteristics TA = 25°C, unless otherwise noted.
Efficiency, VOUT = 5V
100
VIN = 12V
90
80
70
VIN = 24V
VIN = 36V
60 VIN = 48V
50
40
VOUT = 5V
R1 = 1M
30 R2 = 309k
0 0.2
0.4 0.6 0.8
LOAD CURRENT (A)
1 1.2
3991 G01
Efficiency, VOUT = 3.3V
90
80
70 VIN = 12V
60 VIN = 24V
50 VIN = 36V
40 VIN = 48V
30
20
10
0
0.01
0.1 1 10 100 1000
LOAD CURRENT (mA)
3991 G04
LT3991 Feedback Voltage
1.205
1.200
1.195
1.190
1.185
1.180
1.175
–55 –25
5 35 65 95
TEMPERATURE (°C)
125 155
3991 G07
Efficiency, VOUT = 3.3V
90 VIN = 12V
80
70 VIN = 24V
60 VIN = 36V
VIN = 48V
50
40
30
20
0 0.2 0.4 0.6 0.8 1 1.2
LOAD CURRENT (A)
3991 G02
No Load Supply Current
100 DIODES, INC.
DFLS2100
10
1
–55 –25
5 35 65 95
TEMPERATURE (°C)
125 155
3991 G05
LT3991-3.3 Output Voltage
3.345
3.330
3.315
3.300
3.285
3.270
3.255
–50 –25
5 35 65 95
TEMPERATURE (°C)
125 155
3991 G28
Efficiency, VOUT = 5V
100
90
VOUT = 5V
R1 = 1M
80 R2 = 309k
70 VIN = 12V
60
50 VIN = 24V
40
30 VIN = 36V
20 VIN = 48V
10
0
0.01
0.1 1 10 100 1000
LOAD CURRENT (mA)
3991 G03
No Load Supply Current
3.0
OUTPUT IN REGULATION
2.5
LT3991-5
2.0
LT3991-3.3
1.5
1.0
5
10 15 20 25 30 35 40 45 50 55
INPUT VOLTAGE (V)
3991 G06
LT3991-5 Output Voltage
5.06
5.04
5.02
5.00
4.98
4.96
4.94
–50 –25
5 35 65 95
TEMPERATURE (°C)
125 155
3991 G29
3991fa
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