protection features to aid in protecting against output shorts,
input/output overvoltage, 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 6A.
The LT3579 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 1.7A, or
–12V at 1.2A from a 5V input. In addition, the LT3579’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 LT3579’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 LT3579.
The LT3579 also features innovative
SHDN
pin circuitry that
allows for slowly varying input signals and an adjustable
undervoltage lockout function. Additional features such
as frequency foldback and soft-start are integrated. The
LT3579 is available in 20-lead TSSOP and 20-pin 4mm
×
5mm QFN packages.
6A, 42V Combined Power Switch
Output Short Circuit Protection
Wide Input Range: 2.5V to 16V Operating,
40V Maximum Transient
LT3579-1: Dual-Phase Capable
Master/Slave (3.4A/2.6A) Switch Design
User Configurable Undervoltage Lockout
Easily Configurable as a Boost, SEPIC, Inverting, or
Flyback Converter
Low V
CESAT
Switch: 250mV at 5.5A (Typical)
Can be Synchronized to External Clock
Can Synchronize other Switching Regulators
High Gain
SHDN
Pin Accepts Slowly Varying Input
Signals
20-Lead TSSOP and 20-Pin 4mm
×
5mm QFN
Packages
APPLICATIONS
n
n
n
n
Local Power Supply
Vacuum Flourescent 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
1MHz, 5V to 12V Boost Converter with Output Short Circuit Protection
V
IN
5V
2.2μH
10μF
130k
FB
GATE
LT3579
SHDN
RT
SYNC GND
86.6k
CLKOUT
V
C
SS
0.1μF
47pF
TEMPERATURE
MONITOR
8k
2.2nF
3579 TA01
Efficiency and Power Loss
100
90
80
EFFICIENCY (%)
70
60
50
40
30
20
0
0.25 0.5 0.75 1 1.25 1.5 1.75
LOAD CURRENT (A)
2
35791f
35791 TA02
3.2
2.8
2.4
POWER LOSS (W)
2.0
1.6
1.2
0.8
0.4
0
V
OUT
12V
1.7A
6.3k
10μF
SW1 SW2
22μF
V
IN
100k
200k
FAULT
V
IN
1
LT3579/LT3579-1
ABSOLUTE MAXIMUM RATINGS
(Note 1)
V
IN
Voltage ................................................. –0.3V to 40V
SW1/SW2 Voltage ..................................... –0.4V to 42V
R
T
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
......................................................... –0.3V to 40V
FAULT
Current .....................................................±0.5mA
CLKOUT ....................................................... –0.3V to 3V
CLKOUT Current ....................................................±1mA
Operating Junction Temperature Range
LT3579E (Notes 2, 4) .........................–40°C to 125°C
LT3579I (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
SW1
SW1
1
2
3
4
5
6
7
8
9
21
GND
20 SYNC
19 SS
18 R
T
17
SHDN
16 CLKOUT
15 SW2
14 SW2
13 SW2
12 SW2
11 SW2
GATE 1
FAULT
2
V
IN
3
SW1 4
SW1 5
SW1 6
7
SW1
8
GND
9 10
GND
SW2
21
GND
TOP VIEW
SYNC
16 R
T
15
SHDN
14 CLKOUT
13 SW2
12 SW2
11 SW2
SS
V
C
FB
20 19 18 17
SW1 10
FE PACKAGE
20-LEAD PLASTIC TSSOP
T
JMAX
= 125°C,
θ
JA
= 38°C/W,
θ
JC
= 10°C/W
EXPOSED PAD (PIN 21) IS GND, MUST BE SOLDERED TO PCB
UFD PACKAGE
20-LEAD (4mm 5mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 34°C/W,
θ
JC
= 2.7°C/W
EXPOSED PAD (PIN 21) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LT3579EFE#PBF
LT3579IFE#PBF
LT3579EUFD#PBF
LT3579IUFD#PBF
LT3579EFE-1#PBF
LT3579IFE-1#PBF
LT3579EUFD-1#PBF
LT3579IUFD-1#PBF
TAPE AND REEL
LT3579EFE#TRPBF
LT3579IFE#TRPBF
LT3579EUFD#TRPBF
LT3579IUFD#TRPBF
LT3579EFE-1#TRPBF
LT3579IFE-1#TRPBF
LT3579EUFD-1#TRPBF
LT3579IUFD-1#TRPBF
PART MARKING*
LT3579FE
LT3579FE
3579
3579
LT3579FE-1
LT3579FE-1
35791
35791
PACKAGE DESCRIPTION
20-Lead Plastic TSSOP
20-Lead Plastic TSSOP
20-Lead (4mm
×
5mm) Plastic QFN
20-Lead (4mm
×
5mm) Plastic QFN
20-Lead Plastic TSSOP
20-Lead Plastic TSSOP
20-Lead (4mm
×
5mm) Plastic QFN
20-Lead (4mm
×
5mm) Plastic QFN
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–40°C to 125°C
–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.
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/
35791f
2
LT3579/LT3579-1
ELECTRICAL CHARACTERISTICS
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 Sync
SYNC Low Level for Sync
SYNC Clock Pulse Duty Cycle
Recommended Minimum SYNC Ratio
f
SYNC
/f
OSC
Minimum Off-Time
Minimum On-Time
SW1 Current Limit
SW Current Sharing, I
SW2
/I
SW1
SW1 + SW2 Current Limit
Switch V
CESAT
SW1 Leakage Current
SW2 Leakage Current
At All Duty Cycles (Note 3)
SW1 and SW2 Tied Together
I
SW2
/I
SW1
= 0.78, At All Duty Cycles (Note 3)
SW1 and SW2 Tied Together, I
SW1
+ I
SW2
= 5.5A
V
SW1
= 5V
V
SW2
= 5V
l
l
l
l
l
l
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).
CONDITIONS
l
MIN
16.2
1.195
3
80.5
81
TYP
2.3
18.7
1.215
9
83.3
83.3
250
70
1.9
0
0.01
MAX
2.5
21.2
1.230
16
85
85.5
UNITS
V
V
V
mV
μA
μA
μmhos
V/V
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
≤ 15V
R
T
= 34kΩ
R
T
= 432kΩ
Compared to Normal f
OSC
Free-Running or Synchronizing
2.4
1
0.05
2.8
225
2500
0.4
mA
μA
%/V
MHz
kHz
ratio
kHz
V
V
%
l
l
l
l
l
2.2
175
200
1.3
20
2.5
200
1/6
V
SYNC
= 0V to 2V
80
3/4
45
55
nS
nS
5.1
9.4
350
1
1
A
A/A
A
mV
μA
μA
3.4
6
4.2
0.78
7.5
250
0.01
0.01
35791f
3
LT3579/LT3579-1
ELECTRICAL CHARACTERISTICS
PARAMETER
Soft-Start Charge Current
Soft-Start Discharge 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
LT3579, T
J
= 25°C
LT3579-1, All T
J
CLKOUT Rise Time
CLKOUT Fall Time
GATE Pull Down Current
GATE Leakage Current
FAULT
Output Voltage Low
FAULT
Leakage Current
FAULT
Input Voltage Low Threshold
FAULT
Input Voltage High Threshold
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 LT3579E 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
LT3579I is guaranteed over the full –40°C to 125°C operating junction
temperature range.
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
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).
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
100
42
50
12
8
800
800
933
933
0.01
150
0.01
700
950
750
1000
1100
1100
1
300
1
800
1050
MAX
11.3
11.3
1.95
85
1.41
1.38
.3
9.5
1.9
60
13.4
0.1
2.3
200
UNITS
μA
μA
V
mV
V
V
V
μA
μA
μA
V
mV
%
%
ns
ns
μA
μA
μA
mV
μA
mV
mV
Soft-Start High Detection Voltage
Soft-Start Low Detection Voltage
SHDN
Minimum Input Voltage High
SHDN
Input Voltage Low
SHDN
Pin Bias Current
CLKOUT Output Voltage High
CLKOUT Output Voltage Low
CLKOUT Duty Cycle
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
