LT3844
High Voltage, Current Mode
Switching Regulator Controller with
Programmable Operating Frequency
FeaTures
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DescripTion
The
LT
®
3844
is a DC/DC controller used for medium power,
low part count, high efficiency supplies. It offers a wide
4V to 60V input range (7.5V minimum start-up voltage)
and can implement step-down, step-up, inverting and
SEPIC topologies.
The LT3844 includes Burst Mode operation, which reduces
quiescent current below 120µA and maintains high effi-
ciency at light loads. An internal high voltage bias regulator
allows for simple biasing.
Additional features include current mode control for fast
line and load transient response; programmable fixed
operating frequency that can be synchronized to an ex-
ternal clock for noise sensitive applications; 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.
The LT3844 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 registered trademark of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Protected by U.S. Patents, including 5731694, 6498466, 6611131
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High Voltage Operation: Up to 60V
Output Voltages Up to 36V (Step Down)
Programmable Constant Frequency: 100kHz to
500kHz
Synchronizable up to 600kHz
Burst Mode
®
Operation: 120µA Supply Current
10µA Shutdown Supply Current
±1.3% Reference Accuracy
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 48V to 12V, 50W
V
IN
36V TO 60V
Efficiency and Power Loss
vs Load Current
90
88
V
IN
= 48V
7
6
EFFICIENCY
5
4
LOSS
3
2
1
0
10
3844 TA01b
68µF
22µF
1M
1000pF
V
IN
SHDN
C
SS
BURST_EN
V
FB
V
C
SYNC
f
SET
0.22µF
BOOST
TG
SW
V
CC
PGND
SENSE
+
SENSE
–
SGND
10
Si7850DP
EFFICIENCY (%)
82.5k
86
84
82
80
78
76
0.1
POWER LOSS (W)
LT3844
1µF
10µH
PDS5100H
0.015
68µF
V
OUT
12V
50W
33µF
14.7k
10k
680p
120pF
130k
R7
49.9k
1
LOAD CURRENT (A)
3844 TA01
3844fc
For more information
www.linear.com/LT3844
1
LT3844
absoluTe MaxiMuM raTings
(Note 1)
pin conFiguraTion
TOP VIEW
V
IN
SHDN
C
SS
BURST_EN
V
FB
V
C
SYNC
f
SET
1
2
3
4
5
6
7
8
17
16 BOOST
15 TG
14 SW
13 V
CC
12 PGND
11 SENSE
+
10 SENSE
–
9
SGND
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
Differential Sense Voltage
SENSE
+
to SENSE
–
......................................1V to –1V
BURST_EN Voltage .................................... 24V to –0.3V
SYNC, V
C
, V
FB
, C
SS
and
SHDN
Voltages ...... 5V to –0.3V
SHDN
Pin Currents ..................................................1mA
Operating Junction Temperature Range (Note 2)
LT3844E (Note 3) .............................. –40°C to 125°C
LT3844I ............................................. –40°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 (PIN 17) IS SGND, MUST BE SOLDERED TO PCB
orDer inForMaTion
LEAD FREE FINISH
LT3844EFE#PBF
LT3844IFE#PBF
TAPE AND REEL
LT3844EFE#TRPBF
LT3844IFE#TRPBF
http://www.linear.com/product/LT3844#orderinfo
PART MARKING
3844EFE
3844IFE
PACKAGE DESCRIPTION
16-Lead Plastic TSSOP
16-Lead Plastic TSSOP
TEMPERATURE RANGE
–40°C to 125°C
–40°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/.
Some packages are available in 500 unit reels through
designated sales channels with #TRMPBF suffix.
elecTrical characTerisTics
PARAMETER
V
IN
Operating Voltage Range (Note 4)
V
IN
Minimum Start Voltage
V
IN
UVLO Threshold (Falling)
V
IN
UVLO Threshold Hysteresis
V
IN
Supply Current
V
IN
Burst Mode Current
V
IN
Shutdown Current
BOOST Operating Voltage Range
BOOST Operating Voltage Range (Note 5)
BOOST UVLO Threshold (Rising)
BOOST UVLO Threshold Hysteresis
BOOST Supply Current (Note 6)
BOOST Burst Mode Current
BOOST Shutdown Current
CONDITIONS
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, R
SET
= 49.9k,
SENSE
–
= SENSE
+
= 10V, SGND = PGND = SW = SYNC = 0V, unless otherwise noted.
MIN
l
l
l
TYP
MAX
60
7.5
4
UNITS
V
V
V
mV
µA
µA
µA
V
V
V
mV
mA
µA
µA
3844fc
4
3.6
3.8
670
20
20
10
V
CC
> 9V
V
BURST_EN
= 0V, V
FB
= 1.35V
V
SHDN
= 0V
V
BOOST
– V
SW
V
BOOST
– V
SW
V
BOOST
– V
SW
V
BURST_EN
= 0V
V
SHDN
= 0V
l
l
15
75
20
5
400
1.4
0.1
0.1
2
For more information
www.linear.com/LT3844
LT3844
elecTrical characTerisTics
PARAMETER
V
CC
Operating Voltage Range (Note 5)
V
CC
Output Voltage
V
CC
UVLO Threshold (Rising)
V
CC
UVLO Threshold Hysteresis
V
CC
Supply Current (Note 6)
V
CC
Burst Mode Current
V
CC
Shutdown Current
V
CC
Current Limit
Error Amp Reference Voltage
V
FB
Pin Input Current
SHDN
Enable Threshold (Rising)
SHDN
Threshold Hysteresis
Sense Pins Common Mode Range
Current Limit Sense Voltage
Input Current
(I
SENSE+
+ I
SENSE–
)
Operating Frequency
l
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, R
SET
= 49.9k,
SENSE
–
= SENSE
+
= 10V, SGND = PGND = SW = SYNC = 0V, unless otherwise noted.
CONDITIONS
Over Full Line and Load Range
l
l
MIN
TYP
8
6.25
500
1.7
95
20
–120
1.231
25
MAX
20
8.3
UNITS
V
V
V
mV
mA
µA
µA
mA
V
V
nA
V
mV
V
mV
µA
µA
µA
l
V
BURST_EN
= 0V
V
SHDN
= 0V
l
2.1
–40
1.224
1.215
1.3
0
90
Measured at V
FB
Pin
l
1.238
1.245
1.4
36
115
V
FB
= 1.231V
l
l
l
1.35
120
100
350
–25
–170
V
SENSE+
– V
SENSE–
V
SENSE(CM)
= 0V
V
SENSE(CM)
= 2V
V
SENSE(CM)
> 4V
290
270
500
100
300
310
330
100
600
kHz
kHz
kHz
kHz
kHz
kΩ
V
µA
µS
dB
µA
V
V
ns
Minimum Programmable Frequency
Maximum Programmable Frequency
External Sync Frequency Range
SYNC Input Resistance
SYNC Voltage Threshold
Soft-Start Capacitor Control Current
Error Amp Transconductance
Error Amp DC Voltage Gain
Error Amp Sink/Source Current
TG Drive On Voltage (Note 7)
TG Drive Off Voltage
TG Drive Rise/Fall Time
Minimum TG Off Time
Minimum TG On Time
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 LT3844 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 LT3844E 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 LT3844I is guaranteed
over the full –40°C to 125°C operating junction temperature range.
C
LOAD
= 2200pF
C
LOAD
= 2200pF
10% to 90% or 90% to 10%, C
LOAD
= 2200pF
l
l
l
40
l
1.4
2
270
340
62
±30
9.8
0.1
40
2
410
l
l
l
350
250
500
350
ns
ns
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 VGS.
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.
3844fc
For more information
www.linear.com/LT3844
3
LT3844
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
50
25
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
3844 G01
3844 G02
3844 G03
V
CC
vs I
CC(LOAD)
8.05
T
A
= 25°C
8
V
CC
vs V
IN
9 I = 20mA
CC
T
A
= 25°C
I
CC
CURRENT LIMIT (mA)
4
5
6
7
8
V
IN
(V)
3844 G04
3844 G05
I
CC
Current Limit vs Temperature
200
175
150
125
100
75
50
–50
8.00
7
V
CC
(V)
7.95
V
CC
(V)
6
5
7.90
4
7.85
3
0
5
10
15 20 25
I
CC(LOAD)
(mA)
30
35
40
9
10
11
12
–25
0
25
50
75
TEMPERATURE (°C)
100
125
3844 G06
V
CC
UVLO Threshold (Rising)
vs Temperature
6.5
V
CC
UVLO THRESHOLD, RISING (V)
25
I
CC
vs V
CC
(SHDN = 0V)
ERROR AMP TRANSCONDUCTANCE (µS)
T
A
= 25°C
Error Amp Transconductance
vs Temperature
350
345
340
335
330
325
320
–50 –25
6.4
20
15
6.2
I
CC
(mA)
6.3
10
5
6.1
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)
3844 G08
50
25
75
0
TEMPERATURE (°C)
100
125
3844 G07
3844 G09
4
3844fc
For more information
www.linear.com/LT3844
LT3844
Typical perForMance characTerisTics
I
(SENSE+ + SENSE–)
vs
V
SENSE(CM)
400
T
A
= 25°C
OPERATING FREQUENCY (kHz)
300
I
(SENSE
+
+ SENSE
–
)
(µA)
200
100
0
308
306
304
302
300
298
296
294
292
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)
3844 G10
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
290
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
1.227
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
3844 G17
3844 G12
Maximum Current Sense
Threshold vs Temperature
106
CURRENT SENSE THRESHOLD (mV)
104
102
100
98
96
94
–50 –25
V
IN
UVLO THRESHOLD, RISING (V)
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
50
25
75
0
TEMPERATURE (°C)
100
125
4.40
–50 –25
3.76
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
3844 G16
3844 G14
3844 G15
3844fc
For more information
www.linear.com/LT3844
5
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