internal 2A, 42V switch. The LT3580 can be configured
as either a boost, SEPIC or inverting converter. Capable
of generating 12V at 550mA or –12V at 350mA from a 5V
input, the LT3580 is ideal for many local power supply
designs.
The LT3580 has an adjustable oscillator, set by a resistor
from the RT pin to ground. Additionally, the LT3580 can
be synchronized to an external clock. The free running or
synchronized switching frequency range of the part can
be set between 200kHz and 2.5MHz.
The LT3580 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 LT3580 is available in tiny 3mm
×
3mm 8-lead DFN and 8-lead MSOP packages.
L,
LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
2A Internal Power Switch
Adjustable Switching Frequency
Single Feedback Resistor Sets V
OUT
Synchronizable to External Clock
High Gain
SHDN
Pin Accepts Slowly Varying
Input Signals
Wide Input Voltage Range: 2.5V to 32V
Low V
CESAT
Switch: 300mV at 1.5A (Typical)
Integrated Soft-Start Function
Easily Configurable as a Boost or Inverting Converter
User Configurable Undervoltage Lockout (UVLO)
Tiny 8-Lead 3mm
×
3mm DFN and 8-Lead MSOP
Packages
APPLICATIONS
n
n
n
n
n
VFD Bias Supplies
TFT-LCD Bias Supplies
GPS Receivers
DSL Modems
Local Power Supply
TYPICAL APPLICATION
1.2MHz, 5V to 12V Boost Converter Achieves over 88% Efficiency
V
IN
5V
V
IN
SHDN
LT3580
RT
SYNC
2.2μF
75k
SS
0.1μF
FB
VC
10k
1nF
3580 TA01
Efficiency and Power Loss
95
90
1000
85
POWER LOSS (mW)
EFFICIENCY (%)
80
75
600
70
65
60
200
55
50
0
100
200
300
400
LOAD CURRENT (mA)
500
600
0
400
800
1200
4.2μH
V
OUT
12V
550mA
SW
GND
130k
10μF
3580 TA01b
3580fc
1
LT3580
ABSOLUTE MAXIMUM RATINGS
(Note 1)
V
IN
Voltage ................................................. –0.3V to 32V
SW Voltage ................................................ –0.4V to 42V
RT Voltage.................................................... –0.3V to 5V
SS and FB Voltage..................................... –0.3V to 2.5V
VC Voltage ................................................... –0.3V to 2V
SHDN
Voltage ............................................ –0.3V to 32V
SYNC Voltage ............................................ –0.3V to 5.5V
Operating Junction Temperature Range
LT3580E (Notes 2, 5) .........................–40°C to 125°C
LT3580I (Notes 2, 5) ..........................–40°C to 125°C
Storage Temperature Range...................–65°C to 150°C
PIN CONFIGURATION
TOP VIEW
TOP VIEW
FB 1
VC 2
V
IN
3
SW 4
9
8
7
6
5
SYNC
SS
RT
SHDN
FB
VC
V
IN
SW
1
2
3
4
8
7
6
5
SYNC
SS
RT
SHDN
9
MS8E PACKAGE
8-LEAD PLASTIC MSOP
T
JMAX
= 125°C,
θ
JA
= 35°C/W TO 40°C/W
EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
DD PACKAGE
8-LEAD (3mm
×
3mm) PLASTIC DFN
T
JMAX
= 125°C,
θ
JA
= 43°C/W
EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LT3580EDD#PBF
LT3580IDD#PBF
LT3580EMS8E#PBF
LT3580IMS8E#PBF
TAPE AND REEL
LT3580EDD#TRPBF
LT3580IDD#TRPBF
LT3580EMS8E#TRPBF
LT3580IMS8E#TRPBF
PART MARKING*
LCXY
LCXY
LTDCJ
LTDCJ
PACKAGE DESCRIPTION
8-Lead (3mm
×
3mm) Plastic DFN
8-Lead (3mm
×
3mm) Plastic DFN
8-Lead Plastic MSOP
8-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/
3580fc
2
LT3580
ELECTRICAL CHARACTERISTICS
PARAMETER
Operating Voltage Range
Positive Feedback Voltage
Negative Feedback Voltage
Positive FB Pin Bias Current
Negative FB Pin Bias Current
Error Amplifier Transconductance
Error Amplifier Voltage Gain
Quiescent Current
Quiescent Current in Shutdown
Reference Line Regulation
Switching Frequency, f
OSC
Switching Frequency in Foldback
Switching Frequency Set 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
Switch Current Limit
Switch V
CESAT
Switch Leakage Current
Soft-Start Charging Current
SHDN
Minimum Input
Voltage High
SHDN
Input Voltage Low
SHDN
Pin Bias Current
Minimum Duty Cycle (Note 3)
Maximum Duty Cycle (Notes 3, 4)
I
SW
= 1.5A
V
SW
= 5V
V
SS
= 0.5V
Active Mode,
SHDN
Rising
Active Mode,
SHDN
Falling
Shutdown Mode
V
SHDN
= 3V
V
SHDN
= 1.3V
V
SHDN
= 0V
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
unless otherwise noted. (Note 2)
CONDITIONS
l
l
l
l
l
MIN
2.5
1.195
0
81
81
TYP
1.215
5
83.3
83.3
230
70
MAX
32
1.230
12
85
85.5
UNITS
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
V
SHDN
= 2.5V, Not Switching
V
SHDN
= 0V
2.5V ≤ V
IN
≤ 32V
R
T
= 45.3k
R
T
= 464k
Compared to Normal f
OSC
SYNCing or Free Running
l
l
l
l
l
1
0
0.01
1.8
180
200
1.3
2
200
1/4
1.5
1
0.05
2.2
220
2500
0.4
mA
μA
%/V
MHz
kHz
Ratio
kHz
V
V
%
nS
nS
V
SYNC
= 0V to 2V
35
3/4
60
100
2.2
1.6
2.5
1.9
300
0.01
4
1.27
1.24
6
1.32
1.29
40
11.6
0
65
2.8
2.6
1
8
1.38
1.33
0.3
60
13.4
0.1
A
A
mV
μA
μA
V
V
V
μA
μA
μA
9.7
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 LT3580E 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
LT3580I is guaranteed over the full –40°C to 125°C operating junction
temperature range.
Note 3:
Current limit guaranteed by design and/or correlation to static test.
Note 4:
Current limit measured at equivalent switching frequency of
2.5MHz.
Note 5:
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 above the specified maximum operating
junction temperature may impair device reliability.
3580fc
3
LT3580
TYPICAL PERFORMANCE CHARACTERISTICS
Switch Current Limit at 1MHz
400
2.5
SWITCH CURRENT LIMIT (A)
SATURATION VOLTAGE (mV)
2.0
1.5
1.0
0.5
50
0
10
20
30
40 50 60 70
DUTY CYCLE (%)
80
90
0
0
0
1
0.5
1.5
SWITCH CURRENT (A)
2
3580 G02
T
A
= 25°C unless otherwise specified
Switch Current Limit at Minimum
Duty Cycle
2.5
SWITCH CURRENT (A)
2.0
1.5
1.0
0.5
Switch Saturation Voltage
350
300
250
200
150
100
0
200
400
600
800
SS VOLTAGE (mV)
1000
1200
3580 G01
3580 G03
Switch Current Limit at Minimum
Duty Cycle
3.0
2.5
FB VOLTAGE (V)
2.0
1.5
1.0
0.5
0
–50
1.24
Positive Feedback Voltage
V
OUT
50mV/DIV
AC COUPLED
Switching Waveforms for
Figure 14 Circuit
SWITCH CURRENT LIMIT (A)
1.23
1.22
V
SW
10V/DIV
1.21
1.20
I
L
0.5A/DIV
–25
50
25
0
75
TEMPERATURE (°C)
100
125
200ns/DIV
3580 G06
0
50
TEMPERATURE (°C)
100
3580 G04
1.19
–50
3580 G05
Oscillator Frequency
NORMALIZED OSCILLATOR FREQUENCY (F/F
NOM
)
2.7
2.5
2.3
FREQUENCY (MHz)
2.1
1.9
1.7
1.5
1.3
1.1
–50
R
T
= 75k
50
0
TEMPERATURE (°C)
100
3580 G07
Oscillator Frequency During
Soft-Start
1
T
A
= 35°C
T
A
= 100°C
T
A
= 25°C
2.40
2.38
2.36
V
IN
VOLTAGE (V)
2.34
Internal UVLO
R
T
= 35.7k
2.32
2.30
2.28
2.26
1/2
1/3
1/4
INVERTING
CONFIGURATIONS
0
0
0.2
0.4
0.6
0.8
FB VOLTAGE (V)
1.0
1.2
3580 G08
2.24
BOOSTING
CONFIGURATIONS
2.22
2.20
–50
50
0
TEMPERATURE (°C)
100
3580 G09
3580fc
4
LT3580
TYPICAL PERFORMANCE CHARACTERISTICS
SHDN
Pin Current
30
25
SHDN
PIN CURRENT (μA)
SHDN
PIN CURRENT (μA)
20
15
10
5
100°C
0
0
0.5
1
1.5
SHDN
VOLTAGE (V)
2
3580 G10
T
A
= 25°C unless otherwise specified
Active/Lockout Threshold
1.40
1.38
SHDN
Pin Current
300
–50°C
250
200
150
100
50
0
0
5
20
15
25
10
SHDN
VOLTAGE (V)
30
3580 G11
20°C
SHDN
VOLTAGE (V)
100°C
1.36
1.34
1.32
1.30
1.28
1.26
1.24
1.22
SHDN
FALLING
SHDN
RISING
–50°C
20°C
1.20
–50
50
0
TEMPERATURE (°C)
100
3580 G12
PIN FUNCTIONS
FB (Pin 1):
Positive and Negative Feedback Pin. For a
boost or inverting converter, tie a resistor from the FB pin
to V
OUT
according to the following equations:
R
FB
=
R
FB
=
RT (Pin 6):
Timing Resistor Pin. Adjusts the switching
frequency. Place a resistor from this pin to ground to set
the frequency to a fixed free running level. Do not float
this pin.
SS (Pin 7):
Soft-Start Pin. Place a soft-start capacitor here.
Upon start-up, the SS pin will be charged by a (nominally)
275k resistor to about 2.2V.
SYNC (Pin 8):
To synchronize the switching frequency to
an outside clock, simply drive this pin with a clock. The
high voltage level of the clock needs to exceed 1.3V, and
the low level should be less 0.4V. Drive this pin to less than
0.4V to revert to the internal free running clock. See the
Applications Information section for more information.
Exposed Pad (Pin 9):
Ground. Must be soldered directly
to local ground plane.
(
V
OUT
1.215
)
6
(
83.3 • 10
V
OUT
+
5mV
83.3 • 10
6
; Boost or SEPIC Converter
)
; Inverting Converter
VC (Pin 2):
Error Amplifier Output Pin. Tie external com-
pensation network to this pin.
V
IN
(Pin 3):
Input Supply Pin. Must be locally bypassed.
SW (Pin 4):
Switch Pin. This is the collector of the internal
NPN Power switch. Minimize the metal trace area con-
nected to this pin to minimize EMI.
SHDN
(Pin 5):
Shutdown Pin. In conjunction with the
UVLO (undervoltage lockout) circuit, this pin is used
to enable/disable the chip and restart the soft-start
sequence. Drive below 1.24V to disable the chip. Drive
above 1.38V to activate chip and restart the soft-start
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