LT3724
High Voltage, Current Mode
Switching Regulator Controller
FEATURES
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DESCRIPTION
The LT
®
3724 is a DC/DC controller used for medium power,
low part count, low cost, high efficiency supplies. It of-
fers a wide 4V-60V input range (7.5V minimum startup
voltage) and can implement step-down, step-up, inverting
and SEPIC topologies.
The LT3724 includes Burst Mode operation, which re-
duces quiescent current below 100μA and maintains
high efficiency at light loads. An internal high voltage bias
regulator allows for simple biasing and can be back driven
to increase efficiency.
Additional features include fixed frequency current mode
control for fast line and load transient response; a gate driver
capable of driving large N-channel MOSFETs; a precision
undervoltage lockout function; 10μA shutdown current;
short-circuit protection; and a programmable soft-start
function that directly controls output voltage slew rates at
startup which limits inrush current, minimizes overshoot
and facilitates supply sequencing.
The LT3724 is available in a 16-lead thermally enhanced
TSSOP package.
L,
LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
Burst Mode is a trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Protected by U.S. Patents including 5731694, 6498466, 6611131.
Wide Input Range: 4V to 60V
Output Voltages up to 36V (Step-Down)
Burst Mode
®
Operation: <100μA Supply Current
10μA Shutdown Supply Current
±1.3% Reference Accuracy
200kHz Fixed Frequency
Drives N-Channel MOSFET
Programmable Soft-Start
Programmable Undervoltage Lockout
Internal High Voltage Regulator for Gate Drive
Thermal Shutdown
Current Limit Unaffected by Duty Cycle
16-Pin Thermally Enhanced TSSOP Package
APPLICATIONS
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Industrial Power Distribution
12V and 42V Automotive and Heavy Equipment
High Voltage Single Board Systems
Distributed Power Systems
Avionics
Telecom Power
TYPICAL APPLICATION
High Voltage Step-Down Regulator
V
IN
30V TO
60V
C
IN
68μF
1M
LT3724
SHDN
68.1k
200k
C
SS
Burst_EN
V
FB
40.2k
V
C
680pF
120pF
4.99k
93.1k
3724 TA01a
Efficiency and Power Loss
vs Load Current
95
12
10
EFFICIENCY
EFFICIENCY (%)
0.025Ω
47μH
V
OUT
24V
75W
C
OUT
330μF
POWER LOSS (W)
85
80
75
LOSS
70
V
IN
= 48V
65
0.1
1
LOAD CURRENT (A)
0
10
3724 TA01b
V
IN
BOOST
TG
SW
SS3H9
V
CC
1μF
PGND
SENSE
+
SENSE
–
0.22μF
10Ω
90
Si7852
8
6
4
2
+
1000pF
SGND
3724fc
1
LT3724
ABSOLUTE MAXIMUM RATINGS
(Note 1)
PIN CONFIGURATION
TOP VIEW
V
IN
NC
SHDN
C
SS
BURST_EN
V
FB
V
C
SGND
1
2
3
4
5
6
7
8
17
16 BOOST
15 TG
14 SW
13 NC
12 V
CC
11 PGND
10 SENSE
+
9
SENSE
–
Input Supply Voltage (V
IN
) ......................... 65V to –0.3V
Boosted Supply Voltage (BOOST) .............. 80V to –0.3V
Switch Voltage (SW)(Note 8) ........................ 65V to –1V
Differential Boost Voltage
(BOOST to SW)...................................... 24V to –0.3V
Bias Supply Voltage (V
CC
) .......................... 24V to –0.3V
SENSE
+
and SENSE
–
Voltages ................... 40V to –0.3V
(SENSE
+
to SENSE
–
)................................... 1V to –1V
BURST_EN Voltage .................................... 24V to –0.3V
V
C
, V
FB
, C
SS
, and
SHDN
Voltages................. 5V to –0.3V
C
SS
and
SHDN
Pin Currents .....................................1mA
Operating Junction Temperature Range (Notes 2, 3)
LT3724E ............................................. –40°C to 125°C
LT3724I .............................................. –40°C to 125°C
LT3724MP.......................................... –55°C to 125°C
Storage Temperature.............................. –65°C to 150°C
Lead Temperature (Soldering, 10 sec) .................. 300°C
FE PACKAGE
16-LEAD PLASTIC TSSOP
T
JMAX
= 125°C,
θ
JA
= 40°C/W,
θ
JC
= 10°C/W
EXPOSED PAD IS SGND (PIN 17), MUST BE SOLDERED TO PCB
ORDER INFORMATION
LEAD FREE FINISH
LT3724EFE#PBF
LT3724IFE#PBF
LEAD BASED FINISH
LT3724MPFE
TAPE AND REEL
LT3724EFE#TRPBF
LT3724IFE#TRPBF
TAPE AND REEL
LT3724MPFE#TR
PART MARKING
3724EFE
3724IFE
PART MARKING*
3724MPFE
PACKAGE DESCRIPTION
16-Lead Plastic TSSOP
16-Lead Plastic TSSOP
PACKAGE DESCRIPTION
16-Lead Plastic TSSOP
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
TEMPERATURE RANGE
–55°C to 125°C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
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/
ELECTRICAL CHARACTERISTICS
SYMBOL
V
IN
PARAMETER
Operating Voltage Range (Note 4)
Minimum Start Voltage
UVLO Threshold (Falling)
UVLO Threshold Hysteresis
V
IN
Supply Current
V
IN
Burst Mode Current
V
IN
Shutdown Current
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 20V, V
CC
= BOOST = BURST_EN = 10V,
SHDN
= 2V,
SENSE
–
= SENSE
+
= 10V, SGND = PGND = SW = 0V, unless otherwise noted.
CONDITIONS
●
●
●
MIN
4
7.5
3.65
TYP
MAX
60
UNITS
V
V
V
mV
μA
μA
μA
3724fc
3.8
670
20
20
10
3.95
I
VIN
V
CC
> 9V
V
BURST_EN
= 0V, V
FB
= 1.35V
V
SHDN
= 0V
15
2
LT3724
ELECTRICAL CHARACTERISTICS
SYMBOL
V
BOOST
PARAMETER
Operating Voltage Range
Operating Voltage Range (Note 5)
UVLO Threshold (Rising)
UVLO Threshold Hysteresis
BOOST Supply Current (Note 6)
BOOST Burst Mode Current
BOOST Shutdown Current
Operating Voltage Range (Note 5)
Output Voltage
UVLO Threshold (Rising)
UVLO Threshold Hysteresis
V
CC
Supply Current (Note 6)
V
CC
Burst Mode Current
V
CC
Shutdown Current
Short-Circuit Current
Error Amp Reference Voltage
Feedback Input Current
Enable Threshold (Rising)
Threshold Hysteresis
Common Mode Range
Current Limit Sense Voltage
Input Current
(I
SENSE+
+ I
SENSE–
)
Operating Frequency
MP Grade
V
FB(SS)
I
SS
g
m
A
V
V
C
I
VC
V
TG
t
TG
t
TG(OFF)
t
TG(ON)
I
SW
Soft-Start Disable Voltage
Soft-Start Disable Hysteresis
Soft-Start Capacitor Control Current
Error Amp Transconductance
Error Amp DC Voltage Gain
Error Amp Output Range
Error Amp Sink/Source Current
Gate Drive Output On Voltage (Note 7) C
LOAD
= 3300pF
Gate Drive Output Off Voltage
C
LOAD
= 3300pF
Gate Drive Rise/Fall Time
Minimum Switch Off Time
Minimum Switch On Time
SW Pin Sink Current
V
SW
= 2V
●
●
●
●
●
●
●
The
l
denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at T
A
= 25°C. V
IN
= 20V, V
CC
= BOOST = BURST_EN = 10V,
SHDN
= 2V,
SENSE
–
= SENSE
+
= 10V, SGND = PGND = SW = 0V, unless otherwise noted.
CONDITIONS
V
BOOST
- V
SW
V
BOOST
- V
SW
V
BOOST
- V
SW
V
BURST_EN
= 0V
V
SHDN
= 0V
Over Full Line and Load Range
●
●
●
●
MIN
TYP
MAX
75
20
UNITS
V
V
V
mV
mA
μA
μA
5
400
1.4
0.1
0.1
8
6.25
500
1.7
80
20
–55
1.231
25
1.3
0
140
1.35
120
150
400
2
–150
190
175
165
200
200
1.185
300
2
275
340
62
1.2
±30
9.8
0.1
60
350
300
300
500
400
210
220
225
1.4
36
175
20
8.3
I
BOOST
V
CC
V
V
V
mV
mA
μA
μA
mA
V
V
nA
V
mV
V
mV
μA
μA
μA
kHz
kHz
kHz
V
mV
μA
μmhos
dB
V
μA
V
V
ns
ns
ns
mA
I
VCC
●
2.1
V
BURST_EN
= 0V
V
SHDN
= 0V
Measured at V
FB
Pin
●
●
–30
1.224
1.215
V
FB
I
FB
V
SHDN
V
SENSE
I
SENSE
1.238
1.245
V
SENSE+
– V
SENSE–
V
SENSE(CM)
= 0V
V
SENSE(CM)
= 2.5V
V
SENSE(CM)
> 4V
f
SW
V
FB
Rising
Zero Current to Current Limit
10% to 90% or 90% to 10%, C
LOAD
= 3300pF
3724fc
3
LT3724
ELECTRICAL CHARACTERISTICS
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 LT3724 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.
Note 3:
The LT3724E 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
LT3724I is guaranteed over the full –40°C to 125°C operating junction
temperature range. The LT3724MP is 100% tested and guaranteed over
the –55°C to 125°C operating junction temperature range.
Note 4:
V
IN
voltages below the start-up threshold (7.5V) are only
supported when the V
CC
is externally driven above 6.5V.
Note 5:
Operating range is dictated by MOSFET absolute maximum V
GS
.
Note 6:
Supply current specification does not include switch drive
currents. Actual supply currents will be higher.
Note 7:
DC measurement of gate drive output “ON” voltage is typically
8.6V. Internal dynamic bootstrap operation yields typical gate “ON”
voltages of 9.8V during standard switching operation. Standard operation
gate “ON” voltage is not tested but guaranteed by design.
Note 8:
The –1V absolute maximum on the SW pin is a transient condition.
It is guaranteed by design and not subject to test.
TYPICAL PERFORMANCE CHARACTERISTICS
Shutdown Threshold (Rising)
vs Temperature
1.38
SHUTDOWN THRESHOLD, FALLING (V)
SHUTDOWN THRESHOLD, RISING (V)
1.37
1.36
1.35
1.34
1.33
1.32
–50 –25
1.26
1.25
1.24
1.23
1.22
1.21
1.20
–50 –25
V
CC
(V)
Shutdown Threshold (Falling)
vs Temperature
8.2
8.1
8.0
7.9
7.8
7.7
7.6
V
CC
vs Temperature
I
CC
= 20mA
0
25
50
75
TEMPERATURE (°C)
100
125
0
25
50
75
TEMPERATURE (°C)
100
125
7.5
–50 –25
0
25
50
75
TEMPERATURE (°C)
100
125
3724 G01
3724 G02
3724 G03
V
CC
vs I
CC(LOAD)
8.2
T
A
= 25°C
8.1
8.0
7
V
CC
(V)
V
CC
(V)
7.9
7.8
7.7
7.6
7.5
0
5
10
15
20
25
30
35
I
CC (LOAD)
(mA)
3724 G04
V
CC
vs V
IN
9
8
I
CC
= 20mA
T
A
= 25°C
I
CC
CURRENT LIMIT (mA)
70
I
CC
Current Limit vs Temperature
60
50
6
5
4
3
40
30
4
5
6
7
8
V
IN
(V)
9
10
11
12
20
–50 –25
0
25
50
75
TEMPERATURE (°C)
100
125
3724 G05
3724 G06
3724fc
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LT3724
TYPICAL PERFORMANCE CHARACTERISTICS
V
CC
UVLO Threshold (Rising)
vs Temperature
6.5
V
CC
UVLO THRESHOLD, RISING (V)
25
I
CC
vs V
CC
(SHDN = 0V)
T
A
= 25°C
ERROR AMP TRANSCONDUCTANCE (μMhos)
350
345
340
335
330
325
Error Amp Transconductance
vs Temperature
6.4
20
6.2
I
CC
(μA)
6.3
15
10
6.1
5
6.0
–50 –25
0
25
50
75
TEMPERATURE (°C)
100
125
0
0
2
4
6
8
10 12 14 16 18 20
V
CC
(V)
3724 G08
320
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
3724 G07
3724 G09
I
(SENSE+ + SENSE–)
vs
V
SENSE (CM)
400
T
A
= 25°C
OPERATING FREQUENCY (kHz)
300
I
(SENSE
+
+ SENSE
–
)
(μA)
200
100
0
230
220
210
200
190
180
Operating Frequency
vs Temperature
1.234
1.233
ERROR AMP REFERENCE (V)
1.232
1.231
1.230
1.229
1.228
Error Amp Reference
vs Temperature
–100
–200
0
0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0
V
SENSE (CM)
(V)
3724 G10
170
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
1.227
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
3724 G11
3724 G12
Maximum Current Sense
Threshold vs Temperature
160
CURRENT SENSE THRESHOLD (mV)
V
IN
UVLO THRESHOLD, RISING (V)
158
156
154
152
150
148
146
144
142
140
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
4.54
4.52
4.50
4.48
4.46
4.44
4.42
V
IN
UVLO Threshold (Rising)
vs Temperature
3.86
V
IN
UVLO THRESHOLD, FALLING (V)
50
25
75
0
TEMPERATURE (°C)
100
125
V
IN
UVLO Threshold (Falling)
vs Temperature
3.84
3.82
3.80
3.78
4.40
–50 –25
3.76
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
3724 G13
3724 G14
3724 G15
3724fc
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