LT3972 Datasheet PDF - Linear Technology

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LT3972
Linear Technology

Part Number LT3972
Description 2.4MHz Step-Down Switching Regulator
Page 24 Pages


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LT3972
33V, 3.5A, 2.4MHz
Step-Down Switching Regulator
with 75µA Quiescent Current
FEATURES
Wide Input Range:
Operation from 3.6V to 33V
Over-Voltage Lockout Protects Circuits
Through 62V Transients
3.5A Maximum Output Current
Low Ripple (<15mVP-P) Burst Mode® Operation:
IQ = 75μA at 12VIN to 3.3VOUT
Adjustable Switching Frequency: 200kHz to 2.4MHz
Low Shutdown Current: IQ < 1μA
Integrated Boost Diode
Synchronizable Between 250kHz to 2MHz
Power Good Flag
Saturating Switch Design: 95mΩ On-Resistance
Output Voltage: 0.79V to 30V
Thermal Protection
Soft-Start Capability
Small 10-Pin Thermally Enhanced MSOP and
(3mm × 3mm) DFN Packages
APPLICATIONS
Automotive Battery Regulation
www.DaDtaiSshtreiebt4uUte.cdomSupply Regulation
Industrial Supplies
Wall Transformer Regulation
DESCRIPTION
The LT®3972 is an adjustable frequency (200kHz to 2.4MHz)
monolithic buck switching regulator that accepts input
voltages up to 33V (62V Maximum). A high efficiency
95mΩ switch is included on the die along with a boost
Schottky diode and the necessary oscillator, control, and
logic circuitry. Current mode topology is used for fast
transient response and good loop stability. Low ripple
Burst Mode operation maintains high efficiency at low
output currents while keeping output ripple below 15mV
in a typical application. In addition, the LT3972 can fur-
ther enhance low output current efficiency by drawing
bias current from the output when VOUT is above 3V.
Shutdown reduces input supply current to less than 1μA
while a resistor and capacitor on the RUN/SS pin provide a
controlled output voltage ramp (soft-start). A power good
flag signals when VOUT reaches 91% of the programmed
output voltage. The LT3972 is available in 10-Pin MSOP
and 3mm × 3mm DFN packages with exposed pads for
low thermal resistance.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
TYPICAL APPLICATION
5V Step-Down Converter
VIN
6.3V TO 33V
TRANSIENT
TO 62V
OFF ON
15k
10μF
680pF
63.4k
VIN
RUN/SS
BD
BOOST
VC LT3972
RT
PG
SYNC
GND
SW
FB
0.47μF 4.7μH
536k
100k
VOUT
5V
3.5A
47μF
3680 TA01
Efficiency
100
VIN = 12V
90
VIN = 30V
80 VIN = 24V
70
60 VOUT = 5V
L = 4.7μH
f = 600kHz
50
0 0.5 1 1.5 2 2.5
OUTPUT CURRENT (A)
3 3.5
3680 TA01a
3972f
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LT3972
ABSOLUTE MAXIMUM RATINGS (Note 1)
VIN, RUN/SS Voltage (Note 5)...................................62V
BOOST Pin Voltage ...................................................56V
BOOST Pin Above SW Pin.........................................30V
FB, RT, VC Voltage.......................................................5V
PG, BD, SYNC Voltage ..............................................30V
Operating Junction Temperature Range (Note 2)
LT3972E.............................................– 40°C to 125°C
LT3972I..............................................– 40°C to 125°C
Storage Temperature Range...................–65°C to 150°C
Lead Temperature (Soldering, 10 sec)
(MSE Only) ....................................................... 300°C
PIN CONFIGURATION
TOP VIEW
BD
BOOST
SW
VIN
RUN/SS
1
2
3
4
5
10 RT
9 VC
11 8 FB
7 PG
6 SYNC
DD PACKAGE
10-LEAD (3mm s 3mm) PLASTIC DFN
θJA = 45°C/W, θJC = 10°C/W
EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB
BD 1
BOOST 2
SW 3
VIN 4
RUN/SS 5
TOP VIEW
11
10 RT
9 VC
8 FB
7 PG
6 SYNC
MSE PACKAGE
10-LEAD PLASTIC MSOP
θJA = 45°C/W, 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
LT3972EDD#PBF
LT3972EDD#TRPBF
LDXR
10-Lead (3mm × 3mm) Plastic DFN –40°C to 125°C
LT3972IDD#PBF
LT3972IDD#TRPBF
LDXR
10-Lead (3mm × 3mm) Plastic DFN –40°C to 125°C
wwwL.DT3a9ta7S2EhMeeStE4#UP.BcoFm
LT3972EMSE#TRPBF
LTDXS
10-Lead Plastic MSOP
–40°C to 125°C
LT3972IMSE#PBF
LT3972IMSE#TRPBF
LTDXS
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/
ELECTRICAL CHARACTERISTICS The denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 10V, VRUN/SS = 10V, VBOOST = 15V, VBD = 3.3V unless otherwise
noted. (Note 2)
PARAMETER
Minimum Input Voltage
VIN Overvoltage Lockout
Quiescent Current from VIN
Quiescent Current from BD
CONDITIONS
VRUN/SS = 0.2V
VBD = 3V, Not Switching
VBD = 0, Not Switching
VRUN/SS = 0.2V
MIN
33
TYP MAX UNITS
3 3.6
V
35 37
V
0.01 0.5
μA
30 65
μA
120 160
μA
0.01 0.5
μA
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LT3972
ELECTRICAL CHARACTERISTICS The denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 10V, VRUN/SS = 10V, VBOOST = 15V, VBD = 3.3V unless otherwise
noted. (Note 2)
PARAMETER
Minimum Bias Voltage (BD Pin)
CONDITIONS
VBD = 3V, Not Switching
VBD = 0, Not Switching
MIN
TYP MAX UNITS
90 130
μA
15
μA
2.7 3
V
Feedback Voltage
FB Pin Bias Current (Note 3)
FB Voltage Line Regulation
Error Amp gm
Error Amp Gain
VFB = 0.8V, VC = 1.2V
4V < VIN < 33V
780
775
790
790
10
0.002
500
2000
800
805
40
0.01
mV
mV
nA
%/V
μMho
VC Source Current
VC Sink Current
VC Pin to Switch Current Gain
VC Clamp Voltage
Switching Frequency
Minimum Switch Off-Time
Switch Current Limit
Switch VCESAT
Boost Schottky Reverse Leakage
Minimum Boost Voltage (Note 4)
BOOST Pin Current
RUN/SS Pin Current
wwwR.DUaNta/SSShIeneptu4tUV.cooltmage High
RUN/SS Input Voltage Low
PG Threshold Offset from Feedback Voltage
PG Hysteresis
PG Leakage
PG Sink Current
SYNC Low Threshold
RT = 8.66k
RT = 29.4k
RT = 187k
Duty Cycle = 5%
ISW = 3.5A
VBD = 0V
ISW = 1A
VRUN/SS = 2.5V
VFB Rising
VPG = 5V
VPG = 0.4V
2.2
1.0
200
4.6
0.2
200
0.5
60
60
5.3
2
2.45 2.7
1.1 1.25
230 260
60 150
5.4 6.2
335
0.02 2
1.5 2
35 50
58
2.5
65
10
0.1 1
800
μA
μA
A/V
V
MHz
MHz
kHz
nS
A
mV
μA
V
mA
μA
V
V
mV
mV
μA
μA
V
SYNC High Threshold
0.7 V
SYNC Pin Bias Current
VSYNC = 0V
0.1 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 LT3972E is guaranteed to meet performance specifications
from 0°C to 125°C. Specifications over the –40°C to 125°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls. The LT3972I specifications are
guaranteed over the –40°C to 125°C temperature range.
Note 3: Bias current flows out of the FB pin.
Note 4: This is the minimum voltage across the boost capacitor needed to
guarantee full saturation of the switch.
Note 5: Absolute Maximum at VIN and RUN/SS Pins is 62V for non-
repetitive 1 minute transients, and 40V for continuous operation.
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LT3972
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C unless otherwise noted.
Efficiency
100
VIN = 12V
90
VIN = 30V
80 VIN = 24V
70
60 VOUT = 5V
L = 4.7μH
f = 600kHz
50
0 0.5 1 1.5 2 2.5
OUTPUT CURRENT (A)
3 3.5
3680 G01
Efficiency
100
Efficiency
100
3.0
90 VIN = 12V
90
2.5
80 VIN = 30V
VIN = 24V
70
60 VOUT = 3.3V
L = 3.3μH
f = 600kHz
50
0 0.5 1 1.5 2 2.5
OUTPUT CURRENT (A)
3 3.5
3680 G02
80 2.0
70 1.5
60
VIN = 12V
VOUT = 5V
L = 4.7μH
f = 600kHz
50
0 0.5 1 1.5 2 2.5
OUTPUT CURRENT (A)
1.0
0.5
3 3.5
3680 G03
No Load Supply Current
130 VOUT = 3.3V
110
90
70
50
30
www.Data1S0heet4U.com
0 5 10 15 20 25
INPUT VOLTAGE (V)
30 35
3680 G04
No Load Supply Current
400
CATCH DIODE: DIODES, INC. PDS360
350 VIN = 12V
300 VOUT = 3.3V
INCREASED SUPPLY
250 CURRENT DUE TO CATCH
DIODE LEAKAGE AT
200 HIGH TEMPERATURE
150
100
50
0
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
3680 G05
Maximum Load Current
5.5
TYPICAL
5.0
4.5
MINIMUM
4.0
3.5
VOUT = 3.3V
3.0 TA = 25°C
L = 4.7μH
f = 600kHz
2.5
5 10
15
20
INPUT VOLTAGE (V)
25
30
3680 G06
Maximum Load Current
5.5
5.0 TYPICAL
4.5
MINIMUM
4.0
3.5
VOUT = 5V
TA = 25°C
L = 4.7μH
f = 600kHz
3.0
5 10
15
20
INPUT VOLTAGE (V)
25
30
3680 G07
4
Switch Current Limit
6.0
5.5
5.0
4.5
4.0
3.5
3.0
0
20 40
60 80
DUTY CYCLE (%)
100
3680 G08
Switch Current Limit
6.5
6.0
5.5 DUTY CYCLE = 10 %
5.0
4.5 DUTY CYCLE = 90 %
4.0
3.5
3.0
2.5
2.0
–50 –25
0 25 50 75 100 125 150
TEMPERATURE (°C)
3680 G09
3972f



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