LT3844 Datasheet PDF - Linear Technology

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LT3844
Linear Technology

Part Number LT3844
Description Current Mode Switching Regulator Controller
Page 24 Pages


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FEATURES
High Voltage, Current Mode
Switching Regulator Controller with
Programmable Operating Frequency
DESCRIPTIO
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
U
APPLICATIO S
Industrial Power Distribution
12V and 42V Automotive and Heavy Equipment
High Voltage Single Board Systems
Distributed Power Systems
Avionics
Telecom Power
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.
TYPICAL APPLICATIO
High Voltage Step-Down Regulator 48V to 12V, 50W
VIN
36V
TO 68μF
60V
130k 14.7k
22μF 1 MEG
VIN
BOOST
SHDN
1000pF
82.5k
CSS
TG
10Ω
SW
10k
680p
BURST_EN
LT3844
VFB
VC
120pF
SYNC
VCC
1μF
PGND
SENSE+
SENSE
fSET SGND
R7
49.9k
0.22μF
Si7850DP
10μH 0.02Ω
PDS5100H
68μF
VOUT
12V
50W
33μF
3844 TA01
Efficiency and Power Loss
vs Load Current
90 7
88 6
86
EFFICIENCY
84
5
4
82 3
LOSS
80 2
78
76
0.1
1
1
LOAD CURRENT (A)
VIN = 48V 0
10
3844 TA01b
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ABSOLUTE AXI U RATI GS PI CO FIGURATIO
(Note 1)
Input Supply Voltage (VIN)......................... 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 (VCC) ......................... 24V to –0.3V
SENSE+ and SENSEVoltages ................... 40V to –0.3V
Differential Sense Voltage
(SENSE+ to SENSE) .................................. 1V to –1V
BURST_EN Voltage .................................... 24V to –0.3V
SYNC, VC, VFB, CSS, and SHDN Voltages ..... 5V to –0.3V
SHDN Pin Currents ................................................. 1mA
Operating Junction Temperature Range (Note 2)
TOP VIEW
VIN 1
SHDN 2
CSS 3
BURST_EN 4
VFB
VC
SYNC
5
6
7
fSET 8
16 BOOST
15 TG
14 SW
17 13 VCC
12 PGND
11 SENSE+
10 SENSE
9 SGND
FE PACKAGE
16-LEAD PLASTIC TSSOP
TJMAX = 125°C, θJA = 40°C/W, θJC = 10°C/W
EXPOSED PAD IS SGND (PIN 17)
MUST BE SOLDERED TO PCB
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
UW U
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/
TEMPERATURE RANGE
–40°C to 125°C
–40°C to 125°C
ELECTRICAL CHARACTERISTICS The denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 20V, VCC = BOOST = BURST_EN = 10V, SHDN = 2V, RSET = 49.9kΩ,
SENSE= SENSE+ = 10V, SGND = PGND = SW = SYNC = 0V, unless otherwise noted.
PARAMETER
VIN Operating Voltage Range (Note 4)
VIN Minimum Start Voltage
VIN UVLO Threshold (Falling)
VIN UVLO Threshold Hysteresis
VIN Supply Current
VIN Burst Mode Current
VIN 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
VCC > 9V
VBURST_EN = 0V, VFB = 1.35V
VSHDN = 0V
VBOOST - VSW
VBOOST - VSW
VBOOST - VSW
VBURST_EN = 0V
VSHDN = 0V
MIN TYP MAX UNITS
4
60
7.5
3.6
3.8
4
670
V
V
V
mV
20 μA
20 μA
10 15
μA
75 V
20 V
5V
400 mV
1.4 mA
0.1 μA
0.1 μA
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ELECTRICAL CHARACTERISTICS The denotes the specifications which apply over the full operating
temperature range, otherwise specifications are at TA = 25°C. VIN = 20V, VCC = BOOST = BURST_EN = 10V, SHDN = 2V, RSET = 49.9kΩ,
SENSE= SENSE+ = 10V, SGND = PGND = SW = SYNC = 0V, unless otherwise noted.
PARAMETER
VCC Operating Voltage Range (Note 5)
VCC Output Voltage
VCC UVLO Threshold (Rising)
VCC UVLO Threshold Hysteresis
VCC Supply Current (Note 6)
VCC Burst Mode Current
VCC Shutdown Current
VCC Current Limit
Error Amp Reference Voltage
VFB Pin Input Current
SHDN Enable Threshold (Rising)
SHDN Threshold Hysteresis
Sense Pins Common Mode Range
Current Limit Sense Voltage
Input Current
(ISENSE+ + ISENSE–)
Operating Frequency
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
CONDITIONS
Over Full Line and Load Range
VBURST_EN = 0V
VSHDN = 0V
Measured at VFB Pin
VFB = 1.231V
VSENSE+ – VSENSE–
VSENSE(CM) = 0V
VSENSE(CM) = 2V
VSENSE(CM) > 4V
MIN
–40
1.224
1.215
1.3
0
90
290
270
500
100
270
CLOAD = 2200pF
CLOAD = 2200pF
10% to 90% or 90% to 10%, CLOAD = 2200pF
TYP
8
6.25
500
1.7
95
20
– 120
1.231
25
1.35
120
100
350
–25
–170
300
40
1.4
2
340
62
±30
9.8
0.1
40
350
250
MAX
20
8.3
2.1
1.238
1.245
1.4
36
115
310
330
100
600
2
410
500
350
UNITS
V
V
V
mV
mA
μA
μA
mA
V
V
nA
V
mV
V
mV
μA
μA
μA
kHz
kHz
kHz
kHz
kHz
kΩ
V
μA
μS
dB
μA
V
V
ns
ns
ns
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.
Note 4: VIN voltages below the start-up threshold (7.5V) are only
supported when the VCC 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.
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LT3844
TYPICAL PERFOR A CE CHARACTERISTICS
Shutdown Threshold (Rising)
vs Temperature
1.38
1.37
1.36
1.35
1.34
1.33
1.32
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3844 G01
Shutdown Threshold (Falling)
vs Temperature
1.26
1.25
1.24
1.23
1.22
1.21
1.20
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3844 G02
VCC vs ICC(LOAD)
8.05
TA = 25°C
8.00
7.95
7.90
7.85
0
5 10 15 20 25 30 35 40
ICC(LOAD) (mA)
3844 G04
VCC UVLO Threshold (Rising)
vs Temperature
6.5
6.4
6.3
6.2
6.1
6.0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3844 G07
VCC vs VIN
9
ICC = 20mA
8 TA = 25°C
7
6
5
4
3
4 5 6 7 8 9 10 11 12
VIN (V)
3844 G05
ICC vs VCC (SHDN = 0V)
25
TA = 25°C
20
15
10
5
0
0 2 4 6 8 10 12 14 16 18 20
VCC (V)
3844 G08
4
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VCC vs Temperature
8.2
8.1
ICC = 20mA
8.0
7.9
7.8
7.7
7.6
7.5
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3844 G03
ICC Current Limit vs Temperature
200
175
150
125
100
75
50
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3844 G06
Error Amp Transconductance
vs Temperature
350
345
340
335
330
325
320
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3844 G09
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