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PDF LT3756-1 Data sheet ( Hoja de datos )
| Número de pieza | LT3756-1 | |
| Descripción | 100VOUT LED Controller | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
n 3000:1 True Color PWMTM Dimming
n Wide Input Voltage Range: 6V to 100V
n Output Voltage Up to 100V
n Constant-Current and Constant-Voltage Regulation
n 100mV High Side Current Sense
n Drives LEDs in Boost, Buck Mode, Buck-Boost Mode,
SEPIC or Flyback Topology
n Adjustable Frequency: 100kHz to 1MHz
n Open LED Protection
n Programmable Undervoltage Lockout with Hysteresis
n Open LED Status Pin (LT3756)
n Frequency Synchronization (LT3756-1)
n PWM Disconnect Switch Driver
n CTRL Pin Provides Analog Dimming
n Low Shutdown Current: <1μA
n Programmable Soft-Start
n Thermally Enhanced 16-Lead QFN (3mm × 3mm)
and MSOP Packages
APPLICATIONS
n High Power LED Applications
n Industrial
n Automotive
LT3756/LT3756-1
100VIN, 100VOUT
LED Controller
DESCRIPTION
The LT®3756 and LT3756-1 are DC/DC controllers designed
to operate as a constant-current source for driving high
current LEDs. They drive a low side external N-channel
power MOSFET from an internal regulated 7V 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 LT3756/LT3756-1 sense 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.
Both parts are available in the 16-lead QFN (3mm × 3mm)
and MSOP packages.
LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
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.
TYPICAL APPLICATION
VIN
8V TO 60V
(100V TRANSIENT)
94% Efficient 30W White LED Headlamp Driver
22μH
4.7μF 1M
VIN
SHDN/UVLO
FB
332k
INTVCC
100k
0.01μF
10k
332k
40.2k
VREF
CTRL
LT3756
ISP
ISN
GATE
OPENLED
SENSE
PWM
SS
RT
28.7k VC
400kHz
1% 10k
PWMOUT
GND INTVCC
4.7μF
0.001μF
0.27Ω
0.018Ω
370mA
1M
14k
4.7μF
30W
LED
STRING
3756 TA01a
100
96
92
88
84
80
0
Efficiency vs VIN
20 40 60
VIN (V)
80
37561 TA01b
37561f
1
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LT3756/LT3756-1
TYPICAL PERFORMANCE CHARACTERISTICS TA = 25°C, unless otherwise noted.
VISP – VISN Threshold vs VCTRL
120
100
80
60
40
20
0
–20
0
0.5 1
VCTRL (V)
1.5 2
3756 G01
VISP – VISN Threshold vs VISP
103
VCTRL = 2V
102
101
100
99
98
97
0
20 40 60
ISP VOLTAGE (V)
80 100
3756 G02
VISP – VISN Threshold
vs Temperature
103
VCTRL = 2V
102
101
100
99
98
97
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
37561 G03
FB Voltage vs Temperature
1.28
1.27
1.26
1.25
1.24
1.23
1.22
1.21
1.20
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
37561 G04
Switching Frequency vs RT
10000
1000
100
10
10
RT (k)
100
37561 G07
VREF Voltage vs Temperature
2.04
2.03
2.02
2.01
2.00
1.99
1.98
1.97
1.96
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
37561 G05
Switching Frequency
vs Temperature
1400
RT = 10k
1300
1200
1100
1000
900
800
700
600
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
37561 G08
VREF Voltage vs VIN
2.04
2.03
2.02
2.01
2.00
1.99
1.98
1.97
1.96
0
20 40 60
VIN (V)
80 100
37561 G06
SHDN/UVLO Hysteresis Current
vs Temperature
2.4
2.2
2.0
1.8
1.6
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
37561 G09
37561f
5
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LT3756/LT3756-1
APPLICATIONS INFORMATION
When VCTRL is higher than 1.1V, the LED current is regu-
lated to:
ILED
=
100mV
RLED
The LED current programming feature can increase total
dimming range by a factor of 10. The CTRL pin should
not be left open (tie to VREF if not used). The CTRL pin
can also be used in conjunction with a thermistor to
provide overtemperature protection for the LED load, or
with a resistor divider to VIN to reduce output power and
switching current when VIN is low. The presence of a time
varying differential voltage signal (ripple) across ISP and
ISN at the switching frequency is expected. The amplitude
of this signal is increased by high LED load current, low
switching frequency and/or a smaller value output filter
capacitor. Some level of ripple signal is acceptable: the
compensation capacitor on the VC pin filters the signal so
the average difference between ISP and ISN is regulated
to the user-programmed value. Ripple voltage amplitude
(peak-to-peak) in excess of 20mV should not cause mis-
operation, but may lead to noticeable offset between the
average value and the user-programmed value.
operation will not exceed 1.1V. For an LED driver of buck or
a buck-boost configuration, the output voltage is typically
level-shifted to a signal with respect to GND as illustrated
in Figure 3. The output can be expressed as:
VOUT
=
VBE
+
1.25
•
R1
R2
ISP/ISN Short-Circuit Protection Feature
The ISP and ISN pins have a protection feature indepen-
dent of the LED current sense feature that operates at
ISN below 3V. The purpose of this feature is to provide
continuous current sensing when ISN is below the LED
current sense common mode range (during start-up or
an output short-circuit fault) to prevent the development
of excessive switching currents that could damage the
power components. The action threshold (150mV, typ) is
above the default LED current sense threshold, so that no
interference will occur over the ISN voltage range where
these two functions overlap. This feature acts in the same
manner as SENSE current limit — it prevents GATE from
going high (switch turn-on) until the ISP/ISN difference
falls below the threshold.
Programming Output Voltage (Constant-Voltage
Regulation) or Open LED/Overvoltage Threshold
For a boost or SEPIC application, the output voltage can
be set by selecting the values of R1 and R2 (see Figure 2)
according to the following equation:
VOUT
=
1.25
•
R1+ R2
R2
For a boost type LED driver, set the resistor from the output
to the FB pin such that the expected VFB during normal
Dimming Control
There are two methods to control the current source for
dimming using the LT3756. One method uses the CTRL
pin to adjust the current regulated in the LEDs. A second
method uses the PWM pin to modulate the current source
between zero and full current to achieve a precisely pro-
grammed average current. To make this method of current
control more accurate, the switch demand current is stored
on the VC node during the quiescent phase when PWM is
low. This feature minimizes recovery time when the PWM
LT3756
FB
3756 F02
VIN
R1
R2
LT3756
FB
3756 F03
+
R1
VOUT
– 100k
RSEN(EXT)
LED
ARRAY
R2
Figure 2. Feedback Resistor Connection
for Boost or SEPIC LED Drivers
Figure 3. Feedback Resistor Connection for
Buck Mode or Buck-Boost Mode LED Driver
37561f
11
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet LT3756-1.PDF ] | |
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