LT3844
High Voltage, Current Mode
Switching Regulator Controller with
Programmable Operating Frequency
DESCRIPTIO
The LT
®
3844 is a DC/DC controller used for medium
power, low part count, high efficiency supplies. It offers
a wide 4V-60V input range (7.5V minimum startup volt-
age) and can implement step-down, step-up, inverting
and SEPIC topologies.
The LT3844 includes Burst Mode operation, which re-
duces quiescent current below 120μA and maintains high
efficiency 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 exter-
nal 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.
, 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.
FEATURES
■
■
■
■
■
■
■
■
■
■
■
■
■
■
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
APPLICATIO S
■
■
■
■
■
■
Industrial Power Distribution
12V and 42V Automotive and Heavy Equipment
High Voltage Single Board Systems
Distributed Power Systems
Avionics
Telecom Power
TYPICAL APPLICATIO
V
IN
36V
TO
60V
High Voltage Step-Down Regulator 48V to 12V, 50W
90
68μF
22μF
1 MEG
V
IN
1000pF
82.5k
SHDN
C
SS
BURST_EN
0.22μF
BOOST
88
6
EFFICIENCY
5
4
3
2
1
V
IN
= 48V
1
LOAD CURRENT (A)
0
10
10Ω
SW
V
CC
LT3844
V
FB
EFFICIENCY (%)
TG
Si7850DP
10μH
1μF
PDS5100H
0.02Ω
PGND
SENSE
+
SENSE
–
SGND
10k
V
C
V
OUT
12V
50W
68μF
33μF
130k
14.7k
680p
120pF
SYNC
f
SET
3844 TA01
R7
49.9k
U
U
U
Efficiency and Power Loss
vs Load Current
7
86
84
82
80
78
76
0.1
POWER LOSS (W)
LOSS
3844 TA01b
3844fa
1
LT3844
ABSOLUTE
(Note 1)
AXI U RATI GS
PI CO FIGURATIO
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
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 IS SGND (PIN 17)
MUST BE SOLDERED TO PCB
ORDER I FOR ATIO
LEAD FREE FINISH
LT3844EFE#PBF
LT3844IFE#PBF
TAPE AND REEL
LT3844EFE#TRPBF
LT3844IFE#TRPBF
PART MARKING
3844EFE
3844IFE
PACKAGE DESCRIPTION
16-Lead Plastic TSSOP
16-Lead Plastic TSSOP
Consult LTC Marketing for parts specified with wider operating temperature ranges.
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/
The
●
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
= 49.9kΩ,
SENSE
–
= SENSE
+
= 10V, SGND = PGND = SW = SYNC = 0V, unless otherwise noted.
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
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
CONDITIONS
●
●
●
ELECTRICAL CHARACTERISTICS
MIN
4
3.6
●
●
●
2
U
16 BOOST
15 TG
14 SW
13 V
CC
12 PGND
11 SENSE
+
10 SENSE
–
9
SGND
U
U
U
U
W W
W
W
U
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
TYP
MAX
60
7.5
4
UNITS
V
V
V
mV
μA
μA
μA
V
V
V
mV
mA
μA
μA
3844fa
3.8
670
20
20
10
15
75
20
5
400
1.4
0.1
0.1
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
The
●
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
= 49.9kΩ,
SENSE
–
= SENSE
+
= 10V, SGND = PGND = SW = SYNC = 0V, unless otherwise noted.
CONDITIONS
Over Full Line and Load Range
●
●
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
●
2.1
V
BURST_EN
= 0V
V
SHDN
= 0V
●
–40
1.224
1.215
1.3
0
90
Measured at V
FB
Pin
●
1.238
1.245
1.4
36
115
V
FB
= 1.231V
●
●
●
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
C
LOAD
= 2200pF
C
LOAD
= 2200pF
10% to 90% or 90% to 10%, C
LOAD
= 2200pF
●
●
●
●
●
40
1.4
2
270
340
62
±30
9.8
0.1
40
●
●
2
410
350
250
500
350
ns
ns
over the full –40°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.
3844fa
3
LT3844
TYPICAL PERFOR A CE CHARACTERISTICS
Shutdown Threshold (Rising)
vs Temperature
1.38
1.26
SHUTDOWN THRESHOLD, FALLING (V)
SHUTDOWN THRESHOLD, RISING (V)
1.37
1.36
1.35
1.34
1.33
1.32
–50 –25
1.23
1.22
1.21
1.20
–50 –25
V
CC
(V)
0
50
25
75
TEMPERATURE (°C)
V
CC
vs I
CC(LOAD)
8.05
T
A
= 25°C
9
8
8.00
7
I
CC
CURRENT LIMIT (mA)
V
CC
(V)
7.95
V
CC
(V)
7.90
4
7.85
3
0
5
10
15 20 25
I
CC(LOAD)
(mA)
30
V
CC
UVLO Threshold (Rising)
vs Temperature
6.5
25
ERROR AMP TRANSCONDUCTANCE (μS)
V
CC
UVLO THRESHOLD, RISING (V)
6.4
I
CC
(μA)
6.3
6.2
6.1
6.0
–50 –25
0
25
50
75
TEMPERATURE (°C)
4
U W
100
3844 G01
Shutdown Threshold (Falling)
vs Temperature
8.2
8.1
8.0
1.24
7.9
7.8
7.7
7.6
V
CC
vs Temperature
I
CC
= 20mA
1.25
125
0
50
25
75
TEMPERATURE (°C)
100
125
7.5
–50 –25
0
25
50
75
TEMPERATURE (°C)
100
125
3844 G02
3844 G03
V
CC
vs V
IN
200
I
CC
= 20mA
T
A
= 25°C
175
150
125
100
75
I
CC
Current Limit vs Temperature
6
5
35
40
4
5
6
7
8
V
IN
(V)
9
10
11
12
50
–50
–25
0
25
50
75
TEMPERATURE (°C)
100
125
3844 G04
3844 G05
3844 G06
I
CC
vs V
CC
(SHDN = 0V)
T
A
= 25°C
350
345
340
335
330
325
Error Amp Transconductance
vs Temperature
20
15
10
5
100
125
0
0
2
4
6
8
10 12 14 16 18 20
V
CC
(V)
3844 G08
320
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
3844 G07
3844 G09
3844fa
LT3844
TYPICAL PERFOR A CE CHARACTERISTICS
I
(SENSE+ + SENSE–)
vs
V
SENSE (CM)
400
T
A
= 25°C
OPERATING FREQUENCY (kHz)
I
(SENSE
+
+ SENSE
–
)
(μA)
304
302
300
298
296
294
292
ERROR AMP REFERENCE (V)
300
200
100
0
–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)
3844 G10
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)
4.52
4.50
4.48
4.46
4.44
4.42
4.40
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
50
25
75
0
TEMPERATURE (°C)
100
125
V
IN
UVLO THRESHOLD, FALLING (V)
PI FU CTIO S
V
IN
(Pin 1):
The V
IN
pin is the main supply pin and should
be decoupled to SGND with a low ESR capacitor located
close to the pin.
SHDN (Pin 2):
The SHDN pin has a precision IC enable
threshold of 1.35V (rising) with 120mV of hysteresis. It is
used to implement an undervoltage lockout (UVLO) cir-
cuit. See Application Information section for implement-
ing a UVLO function. When the SHDN pin is pulled below
a transistor V
BE
(0.7V), a low current shutdown mode is
entered, all internal circuitry is disabled and the V
IN
supply
current is reduced to approximately 9μA. Typical pin input
bias current is <10μA and the pin is internally clamped to
6V.
C
SS
(Pin 3):
The soft-start pin is used to program the
supply soft-start function. Use the following formula to
calculate C
SS
for a given output voltage slew rate:
C
SS
= 2μA(t
SS
/1.231V)
The pin should be left unconnected when not using the
soft-start function.
3844fa
U W
3844 G16
Operating Frequency
vs Temperature
308
306
1.234
1.233
1.232
1.231
1.230
1.229
1.228
Error Amp Reference
vs Temperature
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
V
IN
UVLO Threshold (Rising)
vs Temperature
4.54
3.86
V
IN
UVLO Threshold (Falling)
vs Temperature
3.84
3.82
3.80
3.78
3.76
–50 –25
50
25
75
0
TEMPERATURE (°C)
100
125
3844 G14
3844 G15
U
U
U
5
京公网安备 11010802033920号
Copyright © 2005-2026 EEWORLD.com.cn, Inc. All rights reserved
电子工程世界
