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Linear Technology LT3956 Series Manual

Linear Technology LT3956 Series Manual

80vin, 80vout constant-current, constant-voltage converter

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FeaTures
3000:1 True Color PWM
n
Wide Input Voltage Range: 4.5V to 80V
n
Output Voltage Up to 80V
n
Internal 3.3A/84V Switch
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Constant-Current and Constant-Voltage Regulation
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250mV High Side Current Sense
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Drives LEDs in Boost, Buck Mode, Buck-Boost Mode,
n
SEPIC or Flyback Topology
Adjustable Frequency: 100kHz to 1MHz
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Open LED Protection
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Programmable Undervoltage Lockout with Hysteresis
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Constant-Voltage Loop Status Pin
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PWM Disconnect Switch Driver
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CTRL Pin Adjusts High Side Current Sense Threshold
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Low Shutdown Current: <1µA
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Programmable Soft-Start
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Available in the 36-Lead (5mm × 6mm) QFN Package
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applicaTions
High Power LED
n
Battery Charger
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Accurate Current Limited Voltage Regulator
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Typical applicaTion
94% Efficient 25W White LED Headlamp Driver
V
, 6V TO 60V
IN
(80V TRANSIENT)
2.2µF
332k
V
2
IN
EN/UVLO
100k
V
REF
332k
CTRL
INTV
CC
40.2k
100k
VMODE
PWM
SS
RT
V
C
28.7k
34k
375kHz
47nF
4.7nF
TM
Dimming
22µH
D1
2.2µF
SW
5
PGND
ISP
LT3956
0.68
370mA
ISN
1M
FB
16.2k
PWMOUT
GND
INTV
CC
INTV
CC
4.7µF
Constant-Current,
Constant-Voltage Converter
DescripTion
The LT
3956 is a DC/DC converter designed to operate as
®
a constant-current source and constant-voltage regulator.
It is ideally suited for driving high current LEDs. It features
an internal low side N-channel power MOSFET rated for
84V at 3.3A and driven from an internal regulated 7.15V
supply. The fixed frequency, current-mode architecture
results in stable operation over a wide range of supply
and output voltages. A ground referenced voltage FB pin
serves as the input for several LED protection features,
and also makes it possible for the converter to operate
as a constant-voltage source. A frequency adjust pin
allows the user to program the frequency from 100kHz
to 1MHz to optimize efficiency, performance or external
component size.
The LT3956 senses output current at the high side of the
LED string. High side current sensing is the most flexible
scheme for driving LEDs, allowing boost, buck mode or
buck-boost mode configuration. The PWM input provides
LED dimming ratios of up to 3000:1, and the CTRL input
provides additional analog dimming capability.
L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and
True Color PWM is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners. Protected by U.S. Patents, including 7199560 and 7321203.
25W LED STRING
M1
3956 TA01a
LT3956
80V
, 80V
IN
Efficiency vs V
IN
100
96
92
88
84
80
0
20
40
60
V
(V)
IN
OUT
80
3956 TA01b
3956f


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Summary of Contents for Linear Technology LT3956 Series

  • Page 1 Battery Charger L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and True Color PWM is a trademark of Linear Technology Corporation. All other trademarks are the Accurate Current Limited Voltage Regulator property of their respective owners. Protected by U.S. Patents, including 7199560 and 7321203.
  • Page 2: Absolute Maximum Ratings

    LT3956 absoluTe MaxiMuM raTings pin conFiguraTion (Note 1) TOP VIEW , ISP , ISN ..............80V SW ................84V EN/UVLO (Note 3) .............80V 36 35 34 33 32 31 30 INTV ............V + 0.3V, 8V PWMOUT ..........INTV + 0.3V EN/UVLO CTRL, PWM, VMODE ..........12V INTV FB ................8V , SS ..............3V...
  • Page 3 LT3956 elecTrical characTerisTics denotes the specifications which apply over the full operating temp- erature range, otherwise specifications are at T = 25°C. V = 24V, EN/UVLO = 24V, CTRL = 2V, PWM = 5V, unless otherwise noted. PARAMETER CONDITIONS UNITS SW Pin Leakage SW = 48V µA...
  • Page 4 LT3956 elecTrical characTerisTics denotes the specifications which apply over the full operating temp- erature range, otherwise specifications are at T = 25°C. V = 24V, EN/UVLO = 24V, CTRL = 2V, PWM = 5V, unless otherwise noted. PARAMETER CONDITIONS UNITS Logic Inputs/Outputs PWM Threshold Voltage 0.85...
  • Page 5 LT3956 Typical perForMance characTerisTics = 25°C, unless otherwise noted. FB Regulation Voltage (V vs Temperature Voltage vs Temperature Voltage vs V 2.04 1.28 2.04 2.03 1.27 2.03 2.02 1.26 2.02 2.01 1.25 2.01 2.00 1.24 2.00 1.99 1.23 1.99 1.98 1.22 1.98 1.97...
  • Page 6 LT3956 Typical perForMance characTerisTics = 25°C, unless otherwise noted. Quiescent Current INTV Current Limit vs Switching Frequency vs Temperature INTV Voltage vs Temperature NOT SWITCHING 1000 –50 –25 –50 –25 SWITCHING FREQUENCY (kHz) TEMPERATURE (°C) TEMPERATURE (°C) 3956 G14 3956 G13 3956 G15 SW Pin Current Limit LED Current Sense Threshold...
  • Page 7 LT3956 pin FuncTions NC: No Internal Connection. These pins may be left floating FB: Voltage Loop Feedback Pin. FB is intended for con- or connected to an adjacent pin. stant-voltage regulation or for LED protection/open LED detection. The internal transconductance amplifier with EN/UVLO: Shutdown and Undervoltage Detect Pin.
  • Page 8: Block Diagram

    LT3956 pin FuncTions : Voltage Reference Output Pin (typically 2V). This high. When PWM input goes high again, the VMODE pin pin drives a resistor divider for the CTRL pin, either for will be updated. This pin may be used to report an open analog dimming or for temperature limit/compensation LED fault.
  • Page 9 LT3956 operaTion The LT3956 is a constant-frequency, current mode tor. Likewise, at an ISP/ISN common mode voltage less than 3V, the difference between ISP and ISN is monitored converter with a low side N-channel MOSFET switch. The switch and PWMOUT pin drivers, and other chip to determine if the output is in a short-circuit condition.
  • Page 10 LT3956 applicaTions inForMaTion LED Current Programming INTV Regulator Bypassing and Operation The LED current is programmed by placing an appropri- The INTV pin requires a capacitor for stable operation ate value current sense resistor, R , between the ISP and to store the charge for the switch driver and PWMOUT and ISN pins.
  • Page 11 LT3956 applicaTions inForMaTion 20mV should not cause misoperation, but may lead to Programming Output Voltage (Constant-Voltage noticeable offset between the average value and the user- Regulation) or Open LED/Overvoltage Threshold programmed value. For a boost or SEPIC application, the output voltage can be set by selecting the values of R3 and R4 (see Figure 2) Output Current Capability according to the following equation:...
  • Page 12 LT3956 applicaTions inForMaTion Dimming Control Duty Cycle Considerations There are two methods to control the current source for Switching duty cycle is a key variable defining converter dimming using the LT3956. One method uses the CTRL operation, therefore, its limits must be considered when programming the switching frequency for a particular pin to adjust the current regulated in the LEDs.
  • Page 13 LT3956 applicaTions inForMaTion will be enabled after the device temperature drops 10°C. voltage ripple are key inputs to estimating the capacitor This function is intended to protect the device during value. An X7R type ceramic capacitor is usually the best momentary overload conditions.
  • Page 14 LT3956 applicaTions inForMaTion Output Capacitor Selection it is important to consider diode leakage, which increases with the temperature, from the output during the PWM The selection of the output capacitor depends on the load low interval. Therefore, choose the Schottky diode with and converter configuration, i.e., step-up or step-down sufficiently low leakage current.
  • Page 15 LT3956 applicaTions inForMaTion Loop Compensation interference (EMI), it is important to minimize the area of the high dV/dt switching node between the inductor, SW The LT3956 uses an internal transconductance error ampli- pin and anode of the Schottky rectifier. Use a ground plane fier whose V output compensates the control loop.
  • Page 16: Typical Applications

    LT3956 Typical applicaTions 94% Efficient 25W White LED Headlamp Driver 6V TO 60V 22µH (80V TRANSIENT) M1: VISHAY SILICONIX Si2328DS D1: DIODES INC PDS5100 2.2µF 2.2µF 332k L1: COILTRONICS DR125-220 PGND EN/UVLO C1, C2: MURATA GRM42-2x7R225 100k 332k LT3956 370mA 0.68 CTRL INTV...
  • Page 17 LT3956 Typical applicaTions Buck-Boost Mode LED Driver Efficiency vs V 68µH 9V TO 1µF 4.7µF 4.7µF 100V EN/UVLO 187k 680m LT3956 CTRL INTV 619k 100k LED STRING 350mA VMODE PGND PWMOUT INTV 35.7k 3956 TA03b 300kHz 3.4k INTV 10nF 0.1µF 4.7µF L1: COILCRAFT MSS1038-683 D1: ON SEMICONDUCTOR MBRS3100T3...
  • Page 18 LT3956 Typical applicaTions Efficiency vs V 90% Efficient, 20W SEPIC LED Driver 2.2µF (50V) 33µH 8V TO 250k 4.7µF 10µF EN/UVLO 185k PGND CTRL 0.25 INTV LT3956 100k VMODE STRING 56.2k PWMOUT 3956 TA05b INTV CURRENT DERATED 28.7k FOR V <...
  • Page 19 Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa- tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
  • Page 20 = 42V, True Color PWM Dimming = 3000:1, OUT(MAX) 3000:1 Dimming < 3µA, TSSOP16E Package 3956f Linear Technology Corporation LT 0510 • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 www.linear.com  LINEAR TECHNOLOGY CORPORATION 2010 ● ●...

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