protection features to aid in protecting against output
shorts, input/output overvoltages, and overtemperature
conditions. The part consists of a 42V master switch, and
a 42V slave switch that can be tied together for a total
current limit of 3.3A.
The LT3581 is ideal for many local power supply designs. It
can be easily configured in Boost, SEPIC, Inverting or Flyback
configurations, and is capable of generating 12V at 830mA,
or –12V at 625mA from a 5V input. In addition, the LT3581’s
slave switch allows the part to be configured in high voltage,
high power charge pump topologies that are very efficient
and require fewer components than traditional circuits.
The LT3581’s switching frequency range can be set between
200kHz and 2.5MHz. The part may be clocked internally at
a frequency set by the resistor from the RT pin to ground,
or it may be synchronized to an external clock. A buffered
version of the clock signal is driven out of the CLKOUT
pin, and may be used to synchronize other compatible
switching regulator ICs to the LT3581.
The LT3581 also features innovative
SHDN
pin circuitry
that allows for slowly varying input signals and an adjust-
able undervoltage lockout function. Additional features
such as frequency foldback and soft-start are integrated.
The LT3581 is available in 14-Pin 4mm
×
3mm DFN and
16-Lead MSE packages.
Efficiency and Power Loss vs
Load Current
100
95
90
EFFICIENCY (%)
85
80
75
70
65
60
55
50
3581 TA01
n
n
n
n
n
n
n
n
3.3A, 42V Combined Power Switch
Master/Slave (1.9A/1.4A) Switch Design
Output Short Circuit Protection
Wide Input Range: 2.5V to 22V Operating,
40V Maximum Transient
Switching Frequency Up to 2.5MHz
Easily Configurable as a Boost, SEPIC, Inverting or
Flyback Converter
User Configurable Undervoltage Lockout
Low V
CESAT
Switch: 250mV at 2.75A (Typical)
Can be Synchronized to External Clock
Can Be Synchronized to other Switching Regulators
High Gain
SHDN
Pin Accepts Slowly Varying Input
Signals
14-Pin 4mm
×
3mm DFN and 16-Lead MSE Packages
applicaTions
n
n
n
n
Local Power Supply
Vacuum Fluorescent Display (VFD) Bias Supplies
TFT-LCD Bias Supplies
Automotive Engine Control Unit (ECU) Power
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear
Technology Corporation. All other trademarks are the property of their respective owners.
Protected by U.S. Patents, including 7579816.
Typical applicaTion
Output Short Protected, 5V to 12V Boost Converter Operating at 2MHz
V
IN
5V
18.7k
1.5µH
4.7µF
SW1 SW2
100k
V
IN
FAULT
SHDN
10k
43.2k
RT
SYNC
GND
LT3581
FB
GATE
CLKOUT
V
C
SS
56pF
0.1µF
4.7µF
10.5k
1nF
130k
V
OUT
12V
830mA
6.04k
V
IN
2000
1800
1600
1400
1200
1000
800
600
400
200
0
200
600
800
400
LOAD CURRENT (mA)
0
1000
3581 TA01b
POWER LOSS (mW)
4.7µF
3581f
LT3581
absoluTe MaxiMuM raTings
(Note 1)
V
IN
Voltage ................................................. –0.3V to 40V
SW1/SW2 Voltage ..................................... –0.4V to 42V
RT Voltage ................................................... –0.3V to 5V
SS, FB Voltage .......................................... –0.3V to 2.5V
V
C
Voltage .................................................... –0.3V to 2V
SHDN
Voltage ............................................ –0.3V to 40V
SYNC Voltage............................................ –0.3V to 5.5V
GATE Voltage ............................................. –0.3V to 80V
FAULT
Voltage ............................................ –0.3V to 40V
FAULT
Current .....................................................±500µA
CLKOUT Voltage .......................................... –0.3V to 3V
CLKOUT Current ......................................................1mA
Operating Junction Temperature Range
LT3581E (Notes 2, 4) ......................... –40°C to 125°C
LT3581I (Notes 2, 4) .......................... –40°C to 125°C
Storage Temperature Range .................. –65°C to 150°C
pin conFiguraTion
TOP VIEW
FB
V
C
GATE
FAULT
V
IN
SW1
SW1
1
2
3
4
5
6
7
15
GND
14 SYNC
13 SS
12 RT
11
SHDN
10 CLKOUT
9 SW2
8 SW2
TOP VIEW
FB
V
C
GATE
FAULT
V
IN
SW1
SW1
SW1
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
SYNC
SS
RT
SHDN
CLKOUT
SW2
SW2
SW2
17
GND
DE14 PACKAGE
14-PIN (4mm 3mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 43°C/W,
θ
JC
= 4.3°C/W
EXPOSED PAD (PIN 15) IS GND, MUST BE SOLDERED TO PCB
MSE PACKAGE
16-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 45°C/W,
θ
JC
= 10°C/W
EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB
orDer inForMaTion
LEAD FREE FINISH
LT3581EDE#PBF
LT3581IDE#PBF
LT3581EMSE#PBF
LT3581IMSE#PBF
TAPE AND REEL
LT3581EDE#TRPBF
LT3581IDE#TRPBF
LT3581EMSE#TRPBF
LT3581IMSE#TRPBF
PART MARKING*
3581
3581
3581
3581
PACKAGE DESCRIPTION
14-Lead (4mm
×
3mm) Plastic DFN
14-Lead (4mm
×
3mm) Plastic DFN
16-Lead Plastic MSOP
16-Lead Plastic MSOP
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–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/
3581f
LT3581
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 5V, V
SHDN
= V
IN
, V
FAULT
= V
IN
, unless otherwise noted. (Note 2).
PARAMETER
Minimum Input Voltage
V
IN
Overvoltage Lockout
Positive Feedback Voltage
Negative Feedback Voltage
Positive FB Pin Bias Current
Negative FB Pin Bias Current
Error Amp Transconductance
Error Amp Voltage Gain
Quiescent Current
Quiescent Current in Shutdown
Reference Line Regulation
Switching Frequency, f
OSC
Switching Frequency in Foldback
Switching Frequency Range
SYNC High Level for Synchronization
SYNC Low Level for Synchronization
SYNC Clock Pulse Duty Cycle
Recommended Minimum SYNC Ratio
f
SYNC
/f
OSC
Minimum Off-Time
Minimum On-Time
SW1 Current Limit
Current Sharing (SW2/SW1)
SW1 + SW2 Current Limit
Switch V
CESAT
SW1 Leakage Current
SW2 Leakage Current
At All Duty Cycles, SW2/SW1 = 78% (Note 3)
SW1 & SW2 Tied Together, I
SW1
+ I
SW2
= 2.75A
V
SW1
= 5V
V
SW2
= 5V
l
l
l
elecTrical characTerisTics
CONDITIONS
MIN
l
TYP
2.3
23.5
1.215
9
83.3
83.3
270
70
1.9
0
0.01
MAX
2.5
25
1.230
16
85
85.5
UNITS
V
V
V
mV
µA
µA
µmhos
V/V
22.1
1.195
3
81
81
V
FB
= Positive Feedback Voltage, Current into Pin
V
FB
= Negative Feedback Voltage, Current out of Pin
ΔI = 10μA
Not Switching
V
SHDN
= 0V
2.5V ≤ V
IN
≤ 20V
R
T
= 34k
R
T
= 432k
Compared to Normal f
OSC
Free-Running or Synchronizing
l
l
2.3
1
0.05
2.75
220
2500
0.4
mA
µA
%/V
MHz
kHz
ratio
kHz
V
V
%
l
l
2.25
180
200
1.3
20
2.5
200
1/6
l
l
l
V
SYNC
= 0V to 2V
80
3/4
45
55
ns
ns
3
5.4
1
1
A
%
A
mV
µA
µA
At All Duty Cycles
l
1.9
3.3
2.4
78
4.3
250
0.01
0.01
3581f
LT3581
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 5V, V
SHDN
= V
IN
, V
FAULT
= V
IN
, unless otherwise noted. (Note 2).
PARAMETER
Soft-Start Charge Current
Soft-Start Discharge Current
Soft-Start High Detection Voltage
Soft-Start Low Detection Voltage
SHDN
Minimum Input Voltage High
SHDN
Input Voltage Low
SHDN
Pin Bias Current
CONDITIONS
V
SS
= 30mV, Current Flows Out of SS pin
Part in FAULT, V
SS
= 2.1V, Current Flows into SS Pin
Part in FAULT
Part Exiting FAULT
Active Mode,
SHDN
Rising
Active Mode,
SHDN
Falling
Shutdown Mode
V
SHDN
= 3V
V
SHDN
= 1.3V
V
SHDN
= 0V
C
CLKOUT
= 50pF
C
CLKOUT
= 50pF
T
J
= 25°C
C
CLKOUT
= 50pF
C
CLKOUT
= 50pF
V
GATE
= 3V
V
GATE
= 80V
V
GATE
= 50V, GATE Off
100μA into
FAULT
Pin
V
FAULT
= 40V,
FAULT
Off
l
l
l
l
l
l
l
l
l
l
l
l
elecTrical characTerisTics
MIN
5.7
5.7
1.65
30
1.27
1.24
TYP
8.7
8.7
1.8
50
1.33
1.3
40
11.4
0
2.1
5
42
12
8
MAX
11.3
11.3
1.95
85
1.41
1.38
0.3
60
13.4
0.1
2.3
200
UNITS
µA
µA
V
mV
V
V
V
µA
µA
µA
V
mV
%
ns
ns
9.7
1.9
CLKOUT Output Voltage High
CLKOUT Output Voltage Low
CLKOUT Duty Cycle
CLKOUT Rise Time
CLKOUT Fall Time
GATE Pull Down Current
GATE Leakage Current
FAULT
Output Voltage Low
FAULT
Leakage Current
FAULT
Input Voltage Low
FAULT
Input Voltage High
800
800
933
933
0.01
150
0.01
1100
1100
1
300
1
800
1050
µA
µA
µA
mV
µA
mV
mV
700
950
750
1000
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 LT3581E is guaranteed to meet performance specifications
from 0°C to 125°C. Specifications over the –40°C to 125°C junction
temperature range are assured by design, characterization and correlation
with statistical process controls.
Note 3:
Current limit guaranteed by design and/or correlation to static test.
Note 4:
This IC includes overtemperature protection that is intended
to protect the device during momentary overload conditions. Junction
temperature will exceed 125°C when overtemperature protection is active.
Continuous operation over the specified maximum operating junction
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