LT3481
36V, 2A, 2.8MHz Step-Down
Switching Regulator with
50µA Quiescent Current
FEATURES
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DESCRIPTION
The LT
®
3481 is an adjustable frequency (300kHz to 2.8MHz)
monolithic buck switching regulator that accepts input
voltages up to 34V (36V maximum). A high efficiency
0.18Ω 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 LT3481 can fur-
ther enhance low output current efficiency by drawing
bias current from the output when V
OUT
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 V
OUT
reaches 90% of the programmed
output voltage. The LT3481 is available in 10-Pin MSOP
and 3mm x 3mm DFN packages with exposed pads for
low thermal resistance.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
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Wide Input Range: 3.6V to 34V Operating,
36V Maximum
2A Maximum Output Current
Low Ripple Burst Mode
®
Operation
50μA I
Q
at 12V
IN
to 3.3V
OUT
Output Ripple < 15mV
Adjustable Switching Frequency: 300kHz to 2.8MHz
Low Shutdown Current: I
Q
< 1μA
Integrated Boost Diode
Power Good Flag
Saturating Switch Design: 0.18Ω On-Resistance
1.265V Feedback Reference Voltage
Output Voltage: 1.265V to 20V
Soft-Start Capability
Synchronizable Between 275kHz to 475kHz
Small 10-Pin Thermally Enhanced MSOP and
(3mm x 3mm) DFN Packages
APPLICATIONS
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■
■
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Automotive Battery Regulation
Power for Portable Products
Distributed Supply Regulation
Industrial Supplies
Wall Transformer Regulation
TYPICAL APPLICATION
3.3V Step-Down Converter
V
IN
4.5V TO
34V
OFF ON
16.2k
4.7μF
330pF
60.4k
V
C
RT
PG
GND
BIAS
324k
FB
200k
22μF
40
30
0.0001
LT3481
SW
V
IN
RUN/SS
BD
BOOST
4.7μH
EFFICIENCY (%)
0.47μF
70
60
50
V
IN
= 12V
V
OUT
= 3.3V
L = 4.7μ
F = 800 kHz
0.001
0.01
0.1
LOAD CURRENT (A)
1
10
3481 TA01b
Efficiency
V
OUT
3.3V
2A
90
80
10000.0
1000.0
POWER LOSS (mW)
100.0
10.0
1.0
0.1
0.01
3481 TA01
3481fb
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LT3481
ABSOLUTE MAXIMUM RATINGS
(Note 1)
V
IN
, RUN/SS Voltage .................................................36V
BOOST Pin Voltage ...................................................56V
BOOST Pin Above SW Pin.........................................30V
FB, RT, V
C
Voltage .......................................................5V
BIAS, PG, BD Voltage ................................................30V
Maximum Junction Temperature........................... 125°C
LT3481E, LT3481I ............................................. 125°C
LT3481H ........................................................... 150°C
Operating Temperature Range (Note 2)
LT3481E............................................... –40°C to 85°C
LT3481I.............................................. –40°C to 125°C
LT3481H ............................................ –40°C to 150°C
Storage Temperature Range................... –65°C to 150°C
Lead Temperature (Soldering, 10 sec)
(MSE Only) ....................................................... 300°C
PIN CONFIGURATION
TOP VIEW
TOP VIEW
BD
BOOST
SW
V
IN
RUN/SS
1
2
3
4
5
11
10 RT
9 V
C
8 FB
7 BIAS
6 PG
BD
BOOST
SW
V
IN
RUN/SS
1
2
3
4
5
10
9
8
7
6
RT
V
C
FB
BIAS
PG
11
DD PACKAGE
10-LEAD (3mm 3mm) PLASTIC DFN
EXPOSED PAD (PIN 11) IS GND
MUST BE CONNECTED TO GND
θ
JA
= 43°C/W
MSE PACKAGE
10-LEAD PLASTIC MSOP
EXPOSED PAD (PIN 11) IS GND
MUST BE CONNECTED TO GND
θ
JA
= 40°C/W
ORDER INFORMATION
LEAD FREE FINISH
LT3481EDD#PBF
LT3481IDD#PBF
LT3481HDD#PBF
LT3481EMSE#PBF
LT3481IMSE#PBF
LT3481HMSE#PBF
LEAD BASED FINISH
LT3481EDD
LT3481IDD
LT3481HDD
LT3481EMSE
LT3481IMSE
LT3481HMSE
TAPE AND REEL
LT3481EDD#TRPBF
LT3481IDD#TRPBF
LT3481HDD#TRPBF
LT3481EMSE#TRPBF
LT3481IMSE#TRPBF
LT3481HMSE#TRPBF
TAPE AND REEL
LT3481EDD#TR
LT3481IDD#TR
LT3481HDD#TR
LT3481EMSE#TR
LT3481IMSE#TR
LT3481HMSE#TR
PART MARKING
LBVS
LBVV
LDPT
LTBVT
LTBVW
LTDPV
PART MARKING
LBVS
LBVV
LDPT
LTBVT
LTBVW
LTDPV
PACKAGE DESCRIPTION
10-Lead (3mm
×
3mm) Plastic DFN
10-Lead (3mm
×
3mm) Plastic DFN
10-Lead (3mm
×
3mm) Plastic DFN
10-Lead Plastic MSOP
10-Lead Plastic MSOP
10-Lead Plastic MSOP
PACKAGE DESCRIPTION
10-Lead (3mm
×
3mm) Plastic DFN
10-Lead (3mm
×
3mm) Plastic DFN
10-Lead (3mm
×
3mm) Plastic DFN
10-Lead Plastic MSOP
10-Lead Plastic MSOP
10-Lead Plastic MSOP
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 125°C
–40°C to 150°C
–40°C to 85°C
–40°C to 125°C
–40°C to 150°C
TEMPERATURE RANGE
–40°C to 85°C
–40°C to 125°C
–40°C to 150°C
–40°C to 85°C
–40°C to 125°C
–40°C to 150°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
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/
3481fb
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LT3481
ELECTRICAL CHARACTERISTICS
PARAMETER
Minimum Input Voltage
Quiescent Current from V
IN
V
RUN/SS
= 0.2V
V
BIAS
= 3V, Not Switching
V
BIAS
= 0, Not Switching
Quiescent Current from BIAS
V
RUN/SS
= 0.2V
V
BIAS
= 3V, Not Switching
V
BIAS
= 0, Not Switching
Minimum Bias Voltage
Feedback Voltage
●
●
●
The
●
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 10V, V
RUNS/SS
= 10V V
BOOST
= 15V, V
BIAS
= 3.3V unless otherwise
noted. (Note 2)
CONDITIONS
●
MIN
TYP
3
0.01
22
75
0.01
50
0
2.7
MAX
3.6
0.5
60
120
0.5
120
5
3
1.29
1.3
100
0.02
UNITS
V
μA
μA
μA
μA
μA
μA
V
V
V
nA
%/V
μMho
μA
μA
A/V
V
1.25
1.24
1.265
1.265
30
0.002
330
800
65
85
3.5
2
FB Pin Bias Current (Note 3)
FB Voltage Line Regulation
Error Amp GM
Error Amp Gain
V
C
Source Current
V
C
Sink Current
V
C
Pin to Switch Current Gain
V
C
Clamp Voltage
Switching Frequency
V
FB
= 1.25V, V
C
= 0.4V
4V < V
IN
< 34V
●
RT = 8.66k
RT = 29.4k
RT = 187k
●
2.5
1.25
250
3.2
2.8
1.4
300
130
3.8
360
0.02
3.1
1.55
350
200
4.4
2
2.1
35
10
0.2
MHz
MHz
kHz
nS
A
mV
μA
V
mA
μA
V
V
mV
mV
Minimum Switch Off-Time
Switch Current Limit
Switch V
CESAT
Boost Schottky Reverse Leakage
Minimum Boost Voltage (Note 4)
BOOST Pin Current
RUN/SS Pin Current
RUN/SS Input Voltage High
RUN/SS Input Voltage Low
PG Threshold Offset from Feedback Voltage
PG Hysteresis
PG Leakage
PG Sink Current
V
PG
= 5V
V
PG
= 3V
V
FB
Rising
I
SW
= 1A
V
RUN/SS
= 2.5V
Duty Cycle = 5%
I
SW
= 2A
V
SW
= 10V, V
BIAS
= 0V
●
1.5
18
5
2.5
122
5
0.1
1
μA
μA
●
100
600
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 LT3481E is guaranteed to meet performance specifications
from 0°C to 85°C. Specifications over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls. The LT3481I specifications are
guaranteed over the –40°C to 125°C temperature range. The LT3481H
specifications are guaranteed over the –40°C to 150°C operating
temperature range. High junction temperatures degrade operating
lifetimes. Operating lifetime is derated at junction temperatures greater
than 125°C.
Note 3:
Bias current flows into the FB pin.
Note 4:
This is the minimum voltage across the boost capacitor needed
to guarantee full saturation of the switch.
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LT3481
TYPICAL PERFORMANCE CHARACTERISTICS
Efficiency (V
OUT
= 5.0V)
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
10
0
0.0001
0.001
L: NEC PLC-0745-4R7
f: 800kHz
0.01
0.1
LOAD CURRENT (A)
1
10
3481 G01
Efficiency (V
OUT
= 3.3V)
100
90
85
V
IN
= 7V
80
V
IN
= 24V
V
IN
= 12V
EFFICIENCY (%)
75
70
65
60
L: NEC PLC-0745-4R7
f: 800kHz
0.001
0.01
0.1
LOAD CURRENT (A)
1
10
3481 G02
Efficiency
V
IN
= 12V
V
IN
= 24V
V
IN
= 12V
V
IN
= 24V
EFFICIENCY (%)
90
80
70
60
50
40
30
20
10
0
0.0001
55
50
0
0.5
1
V
OUT
= 3.3V
L = 10μH
LOAD = 1A
2
2.5
1.5
SWITCHING FREQUENCY (MHz)
3
3481 G03
No Load Supply Current
80
70
SUPPLY CURRENT (μA)
SUPPLY CURRENT (μA)
60
50
40
30
20
10
0
0
FRONT PAGE APPLICATION
5
10
25
20
15
INPUT VOLTAGE (V)
30
35
3481 G04
No Load Supply Current
T
A
= 25°C
400
CATCH DIODE: DIODES, INC. PDS360
350
300
250
200
150
100
50
0
–50 –25
0
25 50 75 100
TEMPERATURE (°C)
125 150
3481 G05
Maximum Load Current
4.0
3.5
LOAD CURRENT (A)
3.0
2.5
2.0
1.5
1.0
5
10
20
15
INPUT VOLTAGE (V)
25
30
3481 G06
V
IN
= 12V
V
OUT
= 3.3V
TYPICAL
INCREASED SUPPLY
CURRENT DUE TO CATCH
DIODE LEAKAGE AT
HIGH TEMPERATURE
MINIMUM
V
OUT
= 3.3V
T
A
= 25 °C
L = 4.7μ
f = 800 kHz
Maximum Load Current
4.0
3.5
TYPICAL
LOAD CURRENT (A)
3.0
2.5
MINIMUM
2.0
1.5
1.0
5
10
20
15
INPUT VOLTAGE (V)
25
30
3481 G07
Switch Current Limit
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0
20
60
40
DUTY CYCLE (%)
80
100
3481 G08
Switch Current Limit
4.5
4.0
SWITCH CURRENT LIMIT (A)
3.0
2.5
2.0
1.5
1.0
0.5
0
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
DUTY CYCLE = 90 %
DUTY CYCLE = 10 %
V
OUT
= 5.0V
T
A
= 25 °C
L = 4.7μ
f = 800 kHz
SWITCH CURRENT LIMIT(A)
3481 G09
3481fb
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LT3481
TYPICAL PERFORMANCE CHARACTERISTICS
Switch Voltage Drop
700
600
BOOST PIN CURRENT (mA)
VOLTAGE DROP (mV)
500
400
300
200
100
0
0
500
1000 1500 2000 2500 3000 3500
SWITCH CURRENT (mA)
3481 G10
Boost Pin Current
90
80
FEEDBACK VOLTAGE (V)
70
60
50
40
30
20
10
0
0
500 1000 1500 2000 2500 3000 3500
SWITCH CURRENT (mA)
3481 G11
Feedback Voltage
1.290
1.285
1.280
1.275
1.270
1.265
1.260
1.255
1.250
–50 –25
0
25 50 75 100
TEMPERATURE (°C)
125 150
4381 G12
Switching Frequency
1.20
1.15
1.10
FREQUENCY (MHz)
1.05
1.00
0.95
0.90
0.85
0.80
–50 –25
0
25 50 75 100 125 150
TEMPERATURE (°C)
4381 G13
Frequency Foldback
1200
R
T
= 45.3k
SWITCHING FREQUENCY (kHz)
1000
800
600
400
200
0
0
200
400 600 800 1000 1200 1400
FB PIN VOLTAGE (mV)
3481 G14
Minimum Switch On-Time
140
MINIMUM SWITCH ON TIME (ns)
120
100
80
60
40
20
0
–50 –25
R
T
= 45.3k
0
25 50 75 100 125 150
TEMPERATURE (˚C)
3481 G15
Soft Start
4.0
3.5
SWITCH CURRENT LIMIT (A)
3.0
2.5
2.0
1.5
1.0
0.5
0
0
0.5
2.5
2
1.5
RUN/SS PIN VOLTAGE (V)
1
3
3.5
3481 G16
RUN/SS Pin Current
12
10
8
6
4
2
0
0
5
20
30
15
25
10
RUN/SS PIN VOLTAGE (V)
35
3481 G17
Boost Diode
1.6
1.4
BOOST DIODE V
f
(V)
1.2
1.0
0.8
0.6
0.4
0.2
0
0
1.0
0.5
1.5
BOOST DIODE CURRENT (A)
2.0
3481 G18
RUN/SS PIN CURRENT (μA)
3481fb
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