LT3956
80V , 80V
IN OUT
Constant-Current,
Constant-Voltage Converter
Fae Tseru Dpircse Tnoi
TM
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3000:1 True Color PWM Dimming
The LT 3956 is a DC/DC converter designed to operate as
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Wide Input Voltage Range: 4.5V to 80V
a constant-current source and constant-voltage regulator.
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Output Voltage Up to 80V It is ideally suited for driving high current LEDs. It features
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Internal 3.3A/84V Switch an internal low side N-channel power MOSFET rated for
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Constant-Current and Constant-Voltage Regulation 84V at 3.3A and driven from an internal regulated 7.15V
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supply. The fixed frequency, current-mode architecture
250mV High Side Current Sense
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results in stable operation over a wide range of supply
Drives LEDs in Boost, Buck Mode, Buck-Boost Mode,
and output voltages. A ground referenced voltage FB pin
SEPIC or Flyback Topology
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serves as the input for several LED protection features,
Adjustable Frequency: 100kHz to 1MHz
n and also makes it possible for the converter to operate
Open LED Protection
n as a constant-voltage source. A frequency adjust pin
Programmable Undervoltage Lockout with Hysteresis
n allows the user to program the frequency from 100kHz
Constant-Voltage Loop Status Pin
to 1MHz to optimize efficiency, performance or external
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PWM Disconnect Switch Driver
component size.
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CTRL Pin Adjusts High Side Current Sense Threshold
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Low Shutdown Current: <1A
The LT3956 senses output current at the high side of the
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Programmable Soft-Start
LED string. High side current sensing is the most flexible
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Available in the 36-Lead (5mm 6mm) QFN Package
scheme for driving LEDs, allowing boost, buck mode or
buck-boost mode configuration. The PWM input provides
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LED dimming ratios of up to 3000:1, and the CTRL input
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provides additional analog dimming capability.
High Power LED
n L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
Battery Charger
True Color PWM is a trademark of Linear Technology Corporation. All other trademarks are the
n
Accurate Current Limited Voltage Regulator property of their respective owners. Protected by U.S. Patents, including 7199560 and 7321203.
T lacipy a acilpp Tnoi
Efficiency vs V
94% Efficient 25W White LED Headlamp Driver
IN
V , 6V TO 60V
IN
D1
22H
(80V TRANSIENT)
100
2.2F 2.2F
332k
V SW
IN
s 2 s 5
PGND
EN/UVLO
96
100k
V ISP
REF
332k
LT3956
0.68 370mA
92
CTRL
INTV ISN
CC
40.2k
1M
88
100k
FB
VMODE
25W LED STRING
16.2k
PWM
84
SS
RT PWMOUT
V GND INTV
C CC
80
0 20 60 80
28.7k 40
34k INTV
CC
375kHz
V (V)
IN
47nF 4.7nF 4.7F M1
3956 TA01b
3956 TA01a
3956f
EFFICIENCY (%)LT3956
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(Note 1)
TOP VIEW
V , ISP, ISN ..............................................................80V
IN
SW ............................................................................84V
EN/UVLO (Note 3) .....................................................80V
36 35 34 33 32 31 30
INTV ...................................................... V + 0.3V, 8V
CC IN NC 1 28 ISP
PWMOUT ..................................................INTV + 0.3V EN/UVLO 2 27 ISN
CC
INTV
3
CTRL, PWM, VMODE ................................................12V CC
37
GND
GND FB
4 25
FB ...............................................................................8V
24 GND
V , V , SS ................................................................3V
C REF
V 6 23 PWMOUT
IN
RT ............................................................................1.5V
38
PGND to GND .........................................................0.5V
SW 8 21 SW
SW
Operating Junction Temperature Range
SW SW
9 20
(Note 2) ............................................. 40C to 125C NC 10
12 13 14 15 16 17
Maximum Junction Temperature........................... 125C
Storage Temperature Range ................... 65C to 125C
Lead Temperature (Soldering, 10 sec) .................. 300C
UHE PACKAGE
36-LEAD (5mm s 6mm) PLASTIC QFN
T = 125C, = 43C/W, = 5C/W
JMAX JA JC
EXPOSED PAD (PIN 37) IS GND, MUST BE SOLDERED TO PCB
EXPOSED PAD (PIN 38) IS SW, MUST BE SOLDERED TO PCB
ro D re ni Fro Ma Tnoi
LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE
LT3956EUHE#PBF LT3956EUHE#TRPBF 3956 40C to 125C
36-Lead (5mm 6mm) Plastic QFN
LT3956IUHE#PBF LT3956IUHE#TRPBF 3956 36-Lead (5mm 6mm) Plastic QFN 40C to 125C
Consult LTC Marketing for parts speciefi d with wider operating temperature ranges. *The temperature grade is identiefi d by a label on the shipping container.
For more information on lead free part marking, go to: