FeaTures
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LT3958
High Input Voltage,
Boost, Flyback, SEPIC and
Inverting Converter
DescripTion
The
LT
®
3958
is a wide input range, current mode, DC/DC
converter which is capable of generating either positive
or negative output voltages. It can be configured as either
a boost, flyback, SEPIC or inverting converter. It features
an internal low side N-channel power MOSFET rated for
84V at 3.3A and driven from an internal regulated 7.2V
supply. The fixed frequency, current-mode architecture
results in stable operation over a wide range of supply
and output voltages.
The operating frequency of LT3958 can be set with an
external resistor over a 100kHz to 1MHz range, and can
be synchronized to an external clock using the SYNC pin.
A minimum operating supply voltage of 5V, and a low
shutdown quiescent current of less than 1µA, make the
LT3958 ideally suited for battery-powered systems.
The LT3958 features soft-start and frequency foldback
functions to limit inductor current during start-up.
L,
LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
No R
SENSE
and ThinSOT are trademarks of Analog Devices, Inc. All other trademarks are the
property of their respective owners. Patents pending.
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Wide Input Voltage Range: 5V to 80V
Single Feedback Pin for Positive or Negative
Output Voltage
Internal 3.3A/84V Power Switch
Current Mode Control Provides Excellent Transient
Response
Programmable Operating Frequency (100kHz to
1MHz) with One External Resistor
Synchronizeable to an External Clock
Low Shutdown Current < 1µA
Internal 7.2V Low Dropout Voltage Regulator
Programmable Input Undervoltage Lockout with
Hysteresis
Programmable Soft-Start
Thermally Enhanced QFN (5mm
×
6mm) Package
applicaTions
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Automotive
Telecom
Industrial
Typical applicaTion
High Efficiency Boost Converter
V
IN
12V TO 40V
4.7µF
392k
V
IN
EN/UVLO
53.6k
SGND
SYNC
RT
41.2k
300kHz
SS
0.33µF
VC
10k
10nF
3958 TA01a
Efficiency vs Output Current
V
OUT
48V
0.5A
100
95
EFFICIENCY (%)
90
85
80
75
70
V
IN
= 24V
33µH
4.7µF
×2
GND
SW
LT3958
SENSE1
SENSE2
FBX
INTV
CC
4.7µF
15.8k
464k
0
400
100
200
300
OUTPUT CURRENT (mA)
500
3958 TA01b
3958fa
For more information
www.linear.com/LT3958
1
LT3958
absoluTe MaxiMuM raTings
(Note 1)
pin conFiguraTion
TOP VIEW
SYNC
FBX
NC
NC
SS
VC
28 INTV
CC
27 V
IN
37
SGND
25 EN/UVLO
24 SGND
SENSE1 6
SW 8
SW 9
NC 10
12 13 14 15 16 17
GND
GND
GND
GND
GND
GND
38
SW
23 SGND
21 SW
20 SW
RT
V
IN
, EN/UVLO (Note 5) ..............................................80V
SW ............................................................................84V
INTV
CC
.................................................... V
IN
+ 0.3V, 15V
SYNC ..........................................................................8V
VC, SS.........................................................................3V
RT
...............................................................................................
1.5V
SENSE1, SGND .................. Internally Connected to GND
SENSE2..................................................................±0.3V
FBX ................................................................. –6V to 6V
Operating Temperature Range
(Note 2) ............................................. –40°C to 125°C
Maximum Junction Temperature........................... 125°C
Storage Temperature Range................... –65°C to 125°C
36 35 34 33 32 31 30
NC 1
NC 2
SENSE2 3
SGND 4
UHE PACKAGE
36-LEAD (5mm
×
6mm) PLASTIC QFN
T
JMAX
= 125°C,
θ
JA
= 43°C/W,
θ
JC
= 5°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
orDer inForMaTion
LEAD FREE FINISH
LT3958EUHE#PBF
LT3958IUHE#PBF
TAPE AND REEL
LT3958EUHE#TRPBF
LT3958IUHE#TRPBF
http://www.linear.com/product/LT3958#orderinfo
PART MARKING*
3958
3958
PACKAGE DESCRIPTION
36-Lead (5mm
×
6mm) Plastic QFN
36-Lead (5mm
×
6mm) Plastic QFN
TEMPERATURE RANGE
–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/.
Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
3958fa
2
For more information
www.linear.com/LT3958
LT3958
elecTrical characTerisTics
PARAMETER
V
IN
Operating Range
V
IN
Shutdown I
Q
V
IN
Operating I
Q
V
IN
Operating I
Q
with Internal LDO Disabled
SW Pin Current Limit
SW Pin On Voltage
SENSE2 Input Bias Current
Error Amplifier
FBX Regulation Voltage (V
FBX(REG)
)
FBX Overvoltage Lockout
FBX Pin Input Current
Transconductance g
m
(∆I
VC
/∆FBX)
VC Output Impedance
V
FBX
Line Regulation (∆V
FBX
/[∆V
IN
• V
FBX(REG)
])
VC Current Mode Gain (∆V
VC
/∆V
SENSE
)
VC Source Current
VC Sink Current
Oscillator
Switching Frequency
R
T
= 140k to SGND, FBX = 1.6V, VC = 1.5V
R
T
= 41.2k to SGND, FBX = 1.6V, VC = 1.5V
R
T
= 10.5k to SGND, FBX = 1.6V, VC = 1.5V
FBX = 1.6V
80
270
850
100
300
1000
1.2
200
250
1.5
SS = 0V, Current Out of Pin
l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 24V, EN/UVLO = 24V, SENSE2 = 0V, unless otherwise noted.
CONDITIONS
EN/UVLO = 0V
EN/UVLO = 1.15V
VC = 0.3V, R
T
= 41.2k
VC = 0.3V, R
T
= 41.2k, INTV
CC
= 7.5V
SENSE2 = SENSE1
I
SW
= 2A
Current Out of Pin
FBX > 0V (Note 3)
FBX < 0V (Note 3)
FBX > 0V (Note 4)
FBX < 0V (Note 4)
FBX = 1.6V (Note 3)
FBX = –0.8V (Note 3)
(Note 3)
(Note 3)
FBX > 0V, 5V < V
IN
< 80V (Notes 3, 6)
FBX < 0V, 5V < V
IN
< 80V (Notes 3, 6)
VC = 1.5V, FBX = 0V, Current Out of Pin
FBX = 1.7V
FBX = –0.85V
l
l
l
MIN
5
TYP
0.1
1.6
350
MAX
80
1
6
2.2
400
4.6
UNITS
V
µA
µA
mA
µA
A
mV
µA
3.3
4.0
180
–65
1.569
–0.816
6
7
–10
1.6
–0.800
8
11
70
230
5
0.006
0.005
10
–15
12
11
1.631
–0.784
10
14
100
10
V
V
%
%
nA
nA
µS
MΩ
0.03
0.038
%/V
%/V
V/V
µA
µA
µA
120
330
1200
275
300
0.4
kHz
kHz
kHz
V
ns
ns
RT Voltage
SW Minimum Off-Time
SW Minimum On-Time
SYNC Input Low
SYNC Input High
SS Pull-Up Current
Low Dropout Regulator
INTV
CC
Regulation Voltage
INTV
CC
Undervoltage Lockout Threshold
INTV
CC
Overvoltage Lockout Threshold
–10
7
3.55
11.5
7.2
3.75
0.15
12.8
7.4
4.00
µA
V
V
V
V
Falling INTV
CC
UVLO Hysteresis
3958fa
For more information
www.linear.com/LT3958
3
LT3958
elecTrical characTerisTics
PARAMETER
INTV
CC
Current Limit
INTV
CC
Load Regulation (∆V
INTVCC
/ V
INTVCC
)
Dropout Voltage (V
IN
– V
INTVCC
)
INTV
CC
Current in Shutdown
INTV
CC
Voltage to Bypass Internal LDO
Logic Inputs
EN/UVLO Threshold Voltage Falling
EN/UVLO Voltage Hysteresis
EN/UVLO Input Low Voltage
EN/UVLO Pin Bias Current Low
EN/UVLO Pin Bias Current High
I
VIN
Drops Below 1µA
EN/UVLO = 1.15V
EN/UVLO = 1.33V
1.7
2
10
V
IN
= INTV
CC
= 8V
l
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 24V, EN/UVLO = 24V, SENSE2 = 0V, unless otherwise noted.
CONDITIONS
V
IN
= 80V
V
IN
= 20V
0 < I
INTVCC
< 10mA, V
IN
= 8V
V
IN
= 6V, I
INTVCC
= 10mA, VC = 0V
EN/UVLO = 0V, INTV
CC
= 8V
MIN
19
–1
TYP
24
50
–0.4
0.005
500
16
7.5
1.17
1.22
20
0.4
2.5
100
1.27
0.025
MAX
29
UNITS
mA
mA
%
%/V
mV
µA
V
V
mV
V
µA
nA
INTV
CC
Line Regulation (∆V
INTVCC
/ [∆V
IN
• V
INTVCC
]) 8V < V
IN
< 80V
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 LT3958E is guaranteed to meet performance specifications
from the 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
LT3958I is guaranteed over the full –40°C to 125°C operating junction
temperature range.
Note 3:
The LT3958 is tested in a feedback loop which servos V
FBX
to the
reference voltages (1.6V and –0.8V) with the VC pin forced to 1.3V.
Note 4:
FBX overvoltage lockout is measured at V
FBX(OVERVOLTAGE)
relative
to regulated V
FBX(REG)
.
Note 5:
For 5V < V
IN
< 6V, the EN/UVLO pin must not exceed V
IN
.
Note 6:
EN/UVLO = 1.33V when V
IN
= 5V.
3958fa
4
For more information
www.linear.com/LT3958
LT3958
Typical perForMance characTerisTics
1.604
REGULATED FEEDBACK VOLTAGE (V)
1.602
1.600
1.598
1.596
1.594
1.592
1.590
–50
V
IN
= INTV
CC
= 5V
V
IN
= 8V
T
A
= 25°C, unless otherwise noted.
Quiescent Current
vs Temperature, V
IN
1.8
V
IN
= 80V
V
IN
= 24V
1.6
V
IN
= INTV
CC
= 5V
1.5
Positive Feedback Voltage
vs Temperature, V
IN
REGULATED FEEDBACK VOLTAGE (mV)
V
IN
= 80V
–792
–794
Negative Feedback Voltage
vs Temperature, V
IN
QUIESCENT CURRENT (mA)
125
V
IN
= 24V
–796
–798
–800
–802
–804
–50
V
IN
= INTV
CC
= 5V
V
IN
= 8V
1.7
V
IN
= 24V
V
IN
= 80V
–25
50
25
0
75
TEMPERATURE (°C)
100
125
–25
50
25
0
75
TEMPERATURE (°C)
100
1.4
–50
–25
50
0
25
75
TEMPERATURE (°C)
100
125
3958 G01
3958 G02
3958 G03
Dynamic Quiescent Current
vs Switching Frequency
12
10
8
6
4
2
0
100 200 300 400 500 600 700 800 900 1000
SWITCHING FREQUENCY (kHz)
3958 G04
R
T
vs Switching Frequency
1000
NORMALIZED FREQUENCY (%)
Normalized Switching
Frequency vs FBX
120
100
80
60
40
20
0
–0.8
R
T
(k )
I
Q
(mA)
100
10
0 100 200 300 400 500 600 700 800 900 1000
SWITCHING FREQUENCY (kHz)
3958 G05
–0.4
0
0.4
0.8
FBX VOLTAGE (V)
1.2
1.6
3958 G06
Switching Frequency
vs Temperature
325
320
SWITCHING FREQUENCY (kHz)
315
310
305
300
295
290
285
280
275
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
R
T
= 41.2k
SW PIN CURRENT LIMIT (A)
4.4
4.3
4.2
4.1
4.0
3.9
3.8
3.7
SW Pin Current Limit
vs Temperature
4.4
4.3
SW PIN CURRENT LIMIT (A)
–25
50
25
0
75
TEMPERATURE (°C)
100
125
4.2
4.1
4.0
3.9
3.8
3.7
3.6
SW Pin Current Limit
vs Duty Cycle
3.6
–50
0
20
40
60
DUTY CYCLE (%)
80
100
3958 G09
3958 G07
3958 G08
3958fa
For more information
www.linear.com/LT3958
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