LT3976 Datasheet PDF - Linear Technology

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LT3976
Linear Technology

Part Number LT3976
Description 2MHz Step-Down Switching Regulator
Page 24 Pages


LT3976 datasheet pdf
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Electrical Specifications Subject to Change
LT3976
40V, 5A, 2MHz Step-Down
Switching Regulator with
3.3µA Quiescent Current
FEATURES
n Ultralow Quiescent Current:
3.3μA IQ at 12VIN to 3.3VOUT
n Low Ripple Burst Mode® Operation
Output Ripple < 15mVP-P
n Wide Input Range: Operation from 4.3V to 40V
n 5A Maximum Output Current
n Excellent Start-Up and Dropout Performance
n Adjustable Switching Frequency: 200kHz to 2MHz
n Synchronizable Between 250kHz to 2MHz
n Accurate Programmable Undervoltage Lockout
n Low Shutdown Current: IQ = 700nA
n Power Good Flag
n Soft-Start Capability
n Thermal Shutdown Protection
n Current Limit Foldback with SS Override
n Saturating Switch Design: 75mΩ On Resistance
n Small, Thermally Enhanced 16-Lead MSOP Package
APPLICATIONS
n Automotive Battery Regulation
n Power for Portable Products
n Industrial Supplies
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.
DESCRIPTION
The LT®3976 is an adjustable frequency monolithic buck
switching regulator that accepts a wide input voltage range
up to 40V. Low quiescent current design consumes only
3.3μA 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. The LT3976 can supply up
to 5A of load current and has current limit foldback to
limit power dissipation during short circuit. A low dropout
voltage of 500mV is maintained when the input voltage
drops below the programmed output voltage, such as
during automotive cold crank.
An internally compensated current mode topology is used
for fast transient response and good loop stability. A high
efficiency 75mΩ switch is included on the die along with a
boost Schottky diode and the necessary oscillator, control,
andwww.DataSheet.net/ logic circuitry. An accurate 1.02V threshold enable pin
can be driven directly from a microcontroller or used as a
programmable undervoltage lockout. A capacitor on the
SS pin provides a controlled inrush current (soft-start).
A power good flag signals when VOUT reaches 91.6% of
the programmed output voltage. The LT3976 is available
in a small 16-lead MSOP package with exposed pad for
low thermal resistance.
TYPICAL APPLICATION
VIN
4.3V TO 42V
3.3V Step-Down Converter
OFF ON
10μF
VIN
EN BOOST
PG SW
LT3976
SS
RT
10nF SYNC
130k
OUT
FB
GND
f = 400kHz
0.47μF
3.3μH
PDS540
470pF
1M
10pF
576k
VOUT
3.3V
5A
47μF
w2
3976 TA01a
No-Load Supply Current
8
IN REGULATION
7 VOUT = 3.3V
6
5
4
3
2
1
0
0 5 10 15 20 25 30 35 40
INPUT VOLTAGE (V)
3976 G05
3976p
1
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LT3976
ABSOLUTE MAXIMUM RATINGS
(Note 1)
VIN, EN Voltage (Note 3) ...........................................40V
BOOST Pin Voltage ...................................................55V
BOOST Pin Above SW Pin.........................................30V
FB, RT, SYNC, SS Voltage ...........................................6V
PG Voltage ................................................................30V
OUT Voltage..............................................................16V
Operating Junction Temperature Range (Note 2)
LT3976E............................................. –40°C to 125°C
LT3976I ............................................. –40°C to 125°C
LT3976H ............................................ –40°C to 150°C
Storage Temperature Range .................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec)................... 300°C
PIN CONFIGURATION
FB 1
SS 2
OUT 3
BOOST 4
SW 5
SW 6
SW 7
NC 8
TOP VIEW
17
GND
16 SYNC
15 PG
14 RT
13 EN
12 VIN
11 VIN
10 VIN
9 NC
MSE PACKAGE
16-LEAD PLASTIC MSOP
θJA = 40°C/W
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
TAPE AND REEL
PART MARKING*
PACKAGE DESCRIPTION
TEMPERATURE RANGE
LT3976EMSE#PBF
LT3976EMSE#TRPBF 3976
16-Lead Plastic MSOP
–40°C to 125°C
LT3976IMSE#PBF
LT3976IMSE#TRPBF
3976
16-Lead Plastic MSOP
–40°C to 125°C
LT3976HMSE#PBF
LT3976HMSE#TRPBF 3976
16-Lead Plastic MSOP
–40°C to 150°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. www.DataSheet.net/
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/
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. (Note 2)
PARAMETER
Minimum Input Voltage
Dropout Comparator Threshold
Dropout Comparator Threshold Hysteresis
Quiescent Current from VIN
FB Pin Current
Feedback Voltage
FB Voltage Line Regulation
Switching Frequency
Minimum Switch On-Time
Minimum Switch Off-Time (Note 4)
CONDITIONS
(Note 3)
(VIN – OUT) Falling
VEN Low
VEN High, VSYNC Low
VEN High, VSYNC Low
VFB = 1.5V
4.3V < VIN < 40V (Note 3)
RT = 11.8k
RT = 41.2k
RT = 294k
MIN TYP MAX
l 4 4.3
430 500 570
25
0.7 1.3
1.6 2.7
l 10
l 0.1 12
1.183 1.197 1.212
l 1.173 1.197 1.222
0.0003 0.01
1.8 2.25 2.7
0.8 1 1.2
160 200 240
120
150 200
UNITS
V
mV
mV
μA
μA
μA
nA
V
V
%/V
MHz
MHz
kHz
ns
ns
2
3976p
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LT3976
ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. (Note 2)
PARAMETER
CONDITIONS
MIN TYP MAX
Switch Current Limit
Foldback Switch Current Limit
Switch VCESAT
Switch Leakage Current
VFB = 1V
VFB = 0V
ISW = 1A
7.5 10 12.5
4.8
80
0.02 1
Boost Schottky Forward Voltage
Boost Schottky Reverse Leakage
Minimum Boost Voltage (Note 5)
ISH = 100mA
VREVERSE = 12V
730
0.02 2
l 1.3 1.8
BOOST Pin Current
EN Voltage Threshold
EN Voltage Hysteresis
ISW = 1A, VBOOST – VSW = 3V
EN Falling, VIN ≥ 4.3V
20 32
l 0.92 1.02 1.12
60
EN Pin Current
0.2 20
PG Threshold Offset from VFB
PG Hysteresis as % of Output Voltage
VFB Falling
5 8.4 13
1.7
PG Leakage
PG Sink Current
SYNC Low Threshold
VPG = 3V
VPG = 0.4V
l 125
0.6
0.02
480
1.0
1
SYNC High Threshold
1.18 1.5
SYNC Pin Current
SS Source Current
VSYNC = 6V
VSS = 0.5V
0.1
0.9 1.8 2.6
UNITS
A
A
mV
μA
mV
μA
V
mA
V
mV
nA
%
%
μA
μA
V
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 LT3976E 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
LT3976I is guaranteed over the full –40°C to 125°C operating junction
temperature range. The LT3976H is guaranteed over the full –40°C to
150°C operating junction temperature range. High junction temperatures
degrade operating lifetimes. Operating lifetime is derated at junction
temperatures greater than 125°C. The junction temperature (TJ, in °C) is
calculated from the ambient temperature (TA, in °C) and power dissipation
(PD, in Watts) according to the formula:
TJ = TA + (PD θJA)
where θJA (in °C/W) is the package thermal impedance.
Note 3: Minimum input voltage depends on application circuit.
Note 4: The LT3976 contains circuitry that extends the maximum duty
cyclewww.DataSheet.net/ if there is sufficient voltage across the boost capacitor. See the
Application Information section for more details.
Note 5: This is the minimum voltage across the boost capacitor needed to
guarantee full saturation of the switch.
Note 6: This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed the maximum operating junction temperature
when overtemperature protection is active. Continuous operation above
the specified maximum operating junction temperature may impair device
reliability or permanently damage the device.
3976p
3
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LT3976
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted.
Efficiency at 5VOUT
100
fSW = 800kHz
95 VOUT = 5V
90
85
80
75
70
65
60 12V
55 24V
36V
50
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
LOAD CURRENT (A)
3976 G01
Efficiency at 3.3VOUT
100
FRONT PAGE APPLICATION
90 VOUT = 3.3V
80
70
60
50
40
30
20
10
0
0.01
12V
24V
36V
0.1 1 10 100 1000 10000
LOAD CURRENT (mA)
3976 G04
Reference Voltage
1.230
1.225
1.220
1.215
1.210
1.205
1.200
1.195
1.190
1.185
1.180
1.175
1.170
–55 –25 5 35 65 95
TEMPERATURE (°C)
125 155
3976 G07
Efficiency at 3.3VOUT
100
FRONT PAGE APPLICATION
95 VOUT = 3.3V
90
85
80
75
70
65
60 12V
55 24V
36V
50
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5
LOAD CURRENT (A)
3976 G02
No-Load Supply Current
8
IN REGULATION
7 VOUT = 3.3V
6
5
4
3
www.DataSheet.net/
2
1
0
0 5 10 15 20 25 30 35 40
INPUT VOLTAGE (V)
3976 G05
Load Regulation
0.5
VIN = 12V
0.4 VOUT = 3.3V
0.3
0.2
0.1
0
–0.1
–0.2
–0.3
–0.4
–0.5
0
1 2 34
LOAD CURRENT (A)
5
3976 G08
Efficiency at 5VOUT
100
fSW = 800kHz
90 VOUT = 5V
80
70
60
50
40
30
20
10
0
0.01
12V
24V
36V
0.1 1 10 100 1000 10000
LOAD CURRENT (mA)
3976 G03
No-Load Supply Current
10000
1000
FRONT PAGE APPLICATION
VIN = 12V
VOUT = 3.3V
DUE TO
CATCH DIODE
100 LEAKAGE
10
1
–55 –25
5 35 65 95
TEMPERATURE (°C)
125 155
3876 G06
Line Regulation
0.05
0.04
VIN = 5V
VOUT = 1A
0.03
0.02
0.01
0
–0.01
–0.02
–0.03
–0.04
–0.05
5
10 15 20 25 30
INPUT VOLTAGE (V)
35 40
3976 G09
4
3976p
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