FeaTures
n
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LT3959
Wide Input Voltage Range
Boost/SEPIC/Inverting Converter
with 6A, 40V Switch
DescripTion
The
LT
®
3959
is a wide input range, current mode, DC/DC
controller which is capable of regulating either positive or
negative output voltages from a single feedback pin. It can
be configured as a boost, SEPIC or inverting converter.
It features an internal low side N-channel MOSFET rated
for 6A at 40V and driven from an internal regulated sup-
ply provided from V
IN
or DRIVE. The fixed frequency,
current-mode architecture results in stable operation over
a wide range of supply and output voltages. The operating
frequency of LT3959 can be set over a 100kHz to 1MHz
range with an external resistor, or can be synchronized
to an external clock using the SYNC pin.
The LT3959 features soft-start and frequency foldback
functions to limit inductor current during start-up and
output short-circuit. A window comparator on the FBX
pin reports via the
PGOOD
pin, providing output voltage
status indication.
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
ThinSOT are trademarks of Linear Technology Corporation. All other trademarks are the
property of their respective owners. Protected by U.S. Patents, including 7825665.
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Wide V
IN
Range: 1.6V (2.5V Start-Up) to 40V
Positive or Negative Output Voltage Programming
with a Single Feedback Pin
PGOOD
Output Voltage Status Report
Internal 6A/40V Power Switch
Programmable Soft-Start
Programmable Operating Frequency (100kHz to 1MHz)
with One External Resistor
Synchronizable to an External Clock
Low Shutdown Current < 1µA
INTV
CC
Regulator Supplied from V
IN
or DRIVE
Programmable Input Undervoltage Lockout with
Hysteresis
Thermally Enhanced QFN (5mm × 6mm) and TSSOP
Packages
Automotive
Telecom
Industrial
applicaTions
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Typical applicaTion
2.5V to 24V Input, 12V Output SEPIC Converter
Excellent for Automotive 12V Post Regulator
L1A
C
IN
22µF
50V
×2
150k
4.7µF
50V
100
V
OUT
12V
500mA AT V
IN
= 2.5V
1.5A AT V
IN
> 8V
95
90
EFFICIENCY (%)
85
80
75
70
DRIVE
SYNC
RT
SS
V
C
27.4k
300kHz
0.1µF
7.5k
22nF
4.7µF
3959 TA01a
Efficiency vs Output Current
V
IN
= 12V
V
IN
2.5V TO
24V
124k
V
IN
EN_UVLO
SW
L1B
121k
C
OUT
47µF
16V
×2
LT3959
PGOOD
GND
TIE TO SGND
IF NOT USED
65
105K
60
0
800
600
200
400
OUTPUT CURRENT (mA)
1000
3959 TA01b
FBX
SGND GNDK INTV
CC
15.8K
3959fa
For more information
www.linear.com/LT3959
1
LT3959
absoluTe MaxiMuM raTings
(Note 1)
V
IN
............................................................................40V
EN/UVLO (Note 2) .....................................................40V
DRIVE .......................................................................40V
PGOOD
......................................................................40V
SW ............................................................................40V
INTV
CC
........................................................................8V
SYNC ..........................................................................8V
V
C
, SS .........................................................................3V
RT ............................................................................1.5V
GND, GNDK to SGND .............................................±0.3V
FBX ................................................................. –3V to 3V
Operating Junction Temperature Range (Note 3)
LT3959E/LT3959I .............................. –40°C to 125°C
Storage Temperature Range .................. –65°C to 125°C
pin conFiguraTion
TOP VIEW
PGOOD
INTV
CC
SYNC
NC
FBX
SS
RT
NC
NC
28 DRIVE
37
SGND
27 V
IN
25 EN/UVLO
24 SGND
NC 6
SW 8
SW 9
NC 10
12 13 14 15 16 17
GNDK
GND
GND
GND
GND
GND
38
SW
23 NC
21 SW
20 SW
V
C
FBX
SS
RT
SYNC
PGOOD
V
C
1
2
3
4
5
6
7
8
9
39
SGND
TOP VIEW
38 NC
37 NC
36 NC
35 NC
34 EN/UVLO
33 V
IN
32 DRIVE
31 INTV
CC
30 NC
29 SGND
28 NC
40
SW
27 SW
26 NC
25 NC
24 SW
23 NC
22 GND
21 GND
20 GND
36 35 34 33 32 31 30
NC 1
NC 2
NC 3
SGND 4
SGND 10
NC 11
SW 12
NC 13
NC 14
SW 15
NC 16
GNDK 17
GND 18
GND 19
UHEMA PACKAGE
36-LEAD (5mm
×
6mm) PLASTIC QFN
T
JMAX
=125°C,
θ
JA
= 42°C/W,
θ
JC
= 3°C/W
EXPOSED PAD (PIN 37) IS SGND, MUST BE SOLDERED TO SGND PLANE
EXPOSED PAD (PIN 38) IS SW, MUST BE SOLDERED TO SW PLANE
FE PACKAGE
38-LEAD PLASTIC TSSOP
T
JMAX
=125°C,
θ
JA
= 42°C/W,
θ
JC
= 3°C/W
EXPOSED PAD (PIN 39) IS SGND, MUST BE SOLDERED TO SGND PLANE
EXPOSED PAD (PIN 40) IS SW, MUST BE SOLDERED TO SW PLANE
2
3959fa
For more information
www.linear.com/LT3959
LT3959
orDer inForMaTion
LEAD FREE FINISH
LT3959EUHE#PBF
LT3959IUHE#PBF
LT3959EFE#PBF
LT3959IFE#PBF
TAPE AND REEL
LT3959EUHE#TRPBF
LT3959IUHE#TRPBF
LT3959EFE#TRPBF
LT3959IFE#TRPBF
PART MARKING*
3959
3959
LT3959FE
LT3959FE
PACKAGE DESCRIPTION
36-Lead (5mm × 6mm) Plastic QFN
36-Lead (5mm × 6mm) Plastic QFN
38-Lead Plastic TSSOP
38-Lead Plastic TSSOP
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 nonstandard 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
PARAMETER
V
IN
Operating Voltage
V
IN
Start-Up Voltage
V
IN
Shutdown I
Q
V
IN
Operating I
Q
DRIVE Shutdown Quiescent Current
DRIVE Quiescent Current (Not Switching)
SW Pin Current Limit
SW Pin On Voltage
SW Pin Leakage Current
Error Amplifier
FBX Regulation Voltage (V
FBX(REG)
)
FBX Pin Input Current
Transconductance g
m
(∆I
VC
/∆V
FBX
)
V
C
Output Impedance
FBX Line Regulation [∆V
FBX(REG)
/(∆V
IN
•
V
FBX(REG)
)]
V
C
Source Current
V
C
Sink Current
Oscillator
Switching Frequency
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C, V
IN
= 12V, EN/UVLO = 12V, INTV
CC
= 4.75V, unless otherwise noted.
CONDITIONS
l
MIN
1.6
l
TYP
2.5
0.1
350
MAX
40
2.65
1
6
450
1
2
2.5
8.0
5
UNITS
V
V
µA
µA
µA
µA
µA
mA
A
mV
µA
V
V
nA
nA
µs
MΩ
R
T
= 27.4kΩ, FBX = 0
EN/UVLO < 0.4V
EN/UVLO = 1.15V
EN/UVLO < 0.4V
EN/UVLO = 1.15V
R
T
= 27.4kΩ, DRIVE = 6V
0.1
0.1
2.0
l
6.0
7.0
100
I
SW
= 3A
SW = 40V
FBX > 0V
FBX < 0V
FBX = 1.6V
FBX = –0.8V
FBX = V
FBX(REG)
1.6V < V
IN
< 40V, FBX >0
1.6V < V
IN
< 40V, FBX <0
FBX = 0V, V
C
= 1.3V
FBX = 1.7V, V
C
= 1.3V
FBX = –0.85V, V
C
= 1.3V
R
T
= 27.4k to SGND, V
FBX
= 1.6V
R
T
= 86.6k to SGND, V
FBX
= 1.6V
R
T
= 6.81k to SGND, V
FBX
= 1.6V
FBX = 1.6V, –0.8V
l
l
l
1.580
–0.815
–10
1.6
–0.80
80
240
5
0.02
0.02
–13
13
10
1.620
–0.785
130
10
0.05
0.05
%/V
%/V
µA
µA
µA
250
300
100
1000
1.13
150
150
340
kHz
kHz
kHz
V
ns
ns
3959fa
R
T
Voltage
SW Minimum Off-Time
SW Minimum On-Time
200
200
For more information
www.linear.com/LT3959
3
LT3959
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C, V
IN
= 12V, EN/UVLO = 12V, INTV
CC
= 4.75V, unless otherwise noted.
PARAMETER
SYNC Input Low
SYNC Input High
SS Pull-Up Current
Low Dropout Regulators (DRIVE LDO and V
IN
LDO)
DRIVE LDO Regulation Voltage
V
IN
LDO Regulation Voltage
DRIVE LDO Current Limit
V
IN
LDO Current Limit
DRIVE LDO Load Regulation (∆V
INTVCC
/V
INTVCC
)
V
IN
LDO Load Regulation (∆V
INTVCC
/V
INTVCC
)
DRIVE LDO Line Regulation [∆V
INTVCC
/(V
INTVCC
• ∆V
IN
)]
V
IN
LDO Line Regulation [∆V
INTVCC
/(V
INTVCC
• ∆V
IN
)]
DRIVE LDO Dropout Voltage (V
DRIVE
– V
INTVCC
)
V
IN
LDO Dropout Voltage (V
IN
– V
INTVCC
)
INTV
CC
Undervoltage Lockout Threshold Falling
INTV
CC
Undervoltage Lockout Threshold Rising
INTV
CC
Current in Shutdown
Logic
EN/UVLO Threshold Voltage Falling
EN/UVLO Threshold Voltage Rising Hysteresis
EN/UVLO Input Low Voltage
EN/UVLO Pin Bias Current Low
EN/UVLO Pin Bias Current High
FBX Power Good Threshold Voltage
FBX Overvoltage Threshold
PGOOD
Output Low (V
OL
)
PGOOD
Leakage Current
INTV
CC
Minimum Voltage to Enable
PGOOD
Function
INTV
CC
Minimum Voltage to Enable SYNC Function
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:
For V
IN
below 4V, the EN/UVLO pin must not exceed V
IN
for proper
operation.
I
VIN
< 1μA
EN/UVLO = 1.15V
EN/UVLO = 1.30V
FBX > 0V,
PGOOD
Falling
FBX < 0V,
PGOOD
Falling
FBX > 0V,
PGOOD
Rising
FBX < 0V,
PGOOD
Rising
I
PGOOD
= 250µA
PGOOD
= 40V
l
l
l
elecTrical characTerisTics
CONDITIONS
l
l
MIN
1.5
–14
4.6
3.6
TYP
MAX
0.4
UNITS
V
V
µA
V
V
mA
mA
%
%
SS = 0V, Current Out of Pin
DRIVE = 6V, Not Switching
DRIVE = 0V, Not Switching
INTV
CC
= 4V
DRIVE = 0V, INTV
CC
= 3V
0 < I
INTVCC
< 20mA, DRIVE = 6V
DRIVE = 0V, 0 < I
INTVCC
< 20mA
1.6V < V
IN
< 40V, DRIVE = 6V
DRIVE = 0V, 5V < V
IN
< 40V
DRIVE = 4V, I
INTVCC
= 20mA
V
IN
= 3V, DRIVE = 0V,
I
INTVCC
= 20mA
l
–10.5
4.75
3.75
60
60
–7
4.9
3.9
l
l
–1
–1
–0.6
–0.6
0.03
0.03
0.07
0.07
400
400
2.15
2.45
%/V
%/V
mV
mV
V
V
µA
l
l
l
l
190
190
1.85
2.15
2.0
2.3
25
1.17
1.22
20
EN/UVLO = 0V
1.27
0.4
V
mV
V
µA
nA
V
V
V
V
1.8
2.2
10
V
FBX(REG)
– 0.08
V
FBX(REG)
+ 0.04
V
FBX(REG)
+ 0.12
V
FBX(REG)
– 0.06
210
2.6
100
300
1
2.9
2.9
mV
µA
V
V
2.5
2.5
2.7
2.7
Note 3:
The LT3959E is guaranteed to meet performance specifications
from the 0°C to 125°C operating 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 LT3959I is guaranteed over the full –40°C to 125°C operating junction
temperature range.
Note 4:
The LT3959 is tested in a feedback loop which servos V
FBX
to the
reference voltages (1.6V and –0.8V) with the V
C
pin forced to 1.3V.
4
3959fa
For more information
www.linear.com/LT3959
LT3959
Typical perForMance characTerisTics
FBX Positive Regulation Voltage
vs Temperature
1.62
FBX REGULATION VOLTAGE (V)
FBX REGULATION VOLTAGE (V)
–0.78
T
A
= 25°C, unless otherwise noted.
Quiescent Current
vs Temperature
2.4
2.0
I
Q
(DRIVE)
FBX Negative Regulation Voltage
vs Temperature
1.61
–0.79
1.6
I
Q
(mA)
–0.80
1.2
0.8
–0.81
0.4
–0.82
–50
0.0
–50
I
Q
(V
IN
)
V
IN
= 12V
DRIVE = 6V
1.60
1.59
1.58
–50
–25
25
50
75
0
TEMPERATURE (°C)
100
125
–25
25
50
75
0
TEMPERATURE (°C)
100
125
–25
25
50
75
0
TEMPERATURE (°C)
100
125
3959 G01
3959 G02
3959 G03
Dynamic Quiescent Current
vs Switching Frequency
25
20
DRIVE = 6V
100
90
80
70
I
Q
(mA)
15
R
T
(k)
I
Q
(DRIVE)
10
5
I
Q
(V
IN
)
0
800
600
200
400
SWITCHING FREQUENCY (kHz)
1000
3959 G04
R
T
vs Switching Frequency
Normalized Switching Frequency
vs FBX Voltage
120
NORMALIZED FREQUENCY (%)
100
80
60
40
20
0
–0.8
60
50
40
30
20
10
0
0 100 200 300 400 500 600 700 800 900 1000
SWITCHING FREQUENCY (kHz)
3959 G05
0
–0.4
0
0.4
0.8
1.2
1.6
3959 G06
FBX VOLTAGE (V)
Switching Frequency
vs Temperature
350
7.6
7.4
SW CURRENT LIMIT (A)
7.2
7.0
6.8
6.6
250
–50
SW Current Limit vs Temperature
8.0
7.5
SW CURRENT LIMIT (A)
7.0
6.5
6.0
5.5
5.0
SW Current Limit vs Duty Cycle
SWITCHING FREQUENCY (kHz)
325
300
275
–25
25
50
75
0
TEMPERATURE (°C)
100
125
6.4
–50
–25
0
25
50
75
100
125
0
20
40
60
80
100
3959 G09
TEMPERATURE (°C)
3959 G07
3959 G08
DUTY CYCLE (%)
3959fa
For more information
www.linear.com/LT3959
5
