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PDF LT3492 Data sheet ( Hoja de datos )
| Número de pieza | LT3492 | |
| Descripción | Triple Output LED Driver | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LT3492 (archivo pdf) en la parte inferior de esta página. Total 20 Páginas | ||
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FEATURES
n True Color PWM™ Dimming Delivers Up to 3000:1
Dimming Ratio
n Built-In Gate Driver for PMOS LED Disconnect
n Three Independent Driver Channels with 600mA,
60V Internal Switches
n Operates in Buck, Boost, Buck-Boost Modes
n CTRL Pin Accurately Sets LED Current Sense
Threshold Over a Range of 10mV to 100mV
n Adjustable Frequency: 330kHz to 2.1MHz
n Open LED Protection
n Wide Input Voltage Range:
Operation from 3V to 30V
Transient Protection to 40V
n Surface Mount Components
n 28-Lead (4mm × 5mm) QFN and TSSOP Packages
APPLICATIONS
n RGB Lighting
n Billboards and Large Displays
n Automotive and Avionic Lighting
n Constant-Current Sources
LT3492
Triple Output LED Driver
with 3000:1 PWM Dimming
DESCRIPTION
The LT®3492 is a triple output DC/DC converter designed
to operate as a constant-current source and is ideal for
driving LEDs. The LT3492 works in buck, boost or buck-
boost mode. The LT3492 uses a fixed frequency, current
mode architecture resulting in stable operation over a
wide range of supply and output voltages. A frequency
adjust pin allows the user to program switching frequency
between 330kHz and 2.1MHz to optimize efficiency and
external component size.
The external PWM input provides 3000:1 LED dimming
on each channel. Each of the three channels has a built-in
gate driver to drive an external LED-disconnect P-channel
MOSFET, allowing high dimming range. The output current
range of each channel of the LT3492 is programmed with
an external sense resistor.
The CTRL pin is used to adjust the LED current either for
analog dimming or overtemperature protection.
L, LT, LTC, LTM, Linear Technology and the Linear logo 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, 7321203, and others pending.
wwwT.DYataPShIeCetA4UL.comAPPLICATION
High Dimming Ratio Triple Output Buck-Mode LED Power Supply
PVIN
58V ISP1
330mΩ
ISN1
ISP2
330mΩ
ISN2
TG1 TG2
ISP3
330mΩ
ISN3
TG3
1μF
s3
10 LEDs
0.3A
0.47μF 0.47μF
0.3A
0.3A
0.47μF
33μH
33μH
33μH
VIN
3V TO 24V
1μF
SW1
ISP1-3
ISN1-3
VIN
PWM1-3
SHDN
SW2
LT3492
GND
SW3
TG1-3
VC1-3
VREF
CTRL1-3
FADJ
OVP1-3
150k 10k
49.9k
1.3MHz
680pF
3492 TA01a
3000:1 PWM Dimming at 100Hz
PWM
5V/DIV
ILED
0.2A/DIV
IL
0.5A/DIV
1μs/DIV
3492 TA01b
3492f
1
1 page  
LT3492
TYPICAL PERFORMANCE CHARACTERISTICS (TA = 25°C unless otherwise noted)
Switch Current Limit vs
Temperature
1200
1000
800
600
400
200
0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3492 G04
Switch Frequency vs Temperature
1.4
FADJ = 0.5V
1.3
Reference 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
3492 G05
VISP-VISN Threshold vs CTRL
120
VISP = 24V
100
80
Switch Frequency vs FADJ
2250
2000
1750
1500
1250
1000
750
500
250
0
0 0.2 0.4 0.6 0.8 1.0 1.2
FADJ (V)
3492 G06
VISP-VISN Threshold vs VISP
103
CTRL = 1.2V
102
101
1.2 60 100
40
1.1
20
99
98
1.0
www.DataS–h5e0et4–2U5.com0 25 50 75
TEMPERATURE (°C)
100 125
3492 G07
VISP-VISN Threshold vs
Temperature
103
CTRL = 1.2V
VISP = 24V
102
101
100
99
98
0
0 0.2 0.4 0.6 0.8
CTRL (V)
1 1.2
3492 G08
PMOS Turn On Waveforms
5V
PWM
0V
60V
TG
50V
97
0
10 20 30 40 50 60
VISP (V)
3492 G09
PMOS Turn Off Waveforms
5V
PWM
0V
60V
TG
50V
97
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3492 G10
VISP = 60V
QG FET = 6nC
200ns/DIV
3492 G11
VISP = 60V
QG FET = 6nC
200ns/DIV
3492 G12
3492f
5
5 Page 
LT3492
APPLICATIONS INFORMATION
this capability. Some margin to data sheet limits is included,
along with provision for 200mA inductor ripple current.
For boost mode converters:
IOUT(MAX)
≅
0.4A
VIN(MIN)
VOUT(MAX)
For buck mode converters:
ILED(MAX) ≅ 0.4A
For SEPIC and buck-boost mode converters:
IOUT(MAX)
≅
0.4A
VIN(MIN)
(VOUT(MAX) + VIN(MIN)
)
If some level of analog dimming is acceptable at minimum
supply levels, then the CTRL pin can be used with a resistor
divider to VIN (as shown in the Block Diagram) to provide
a higher output current at nominal VIN levels.
The LED current of each channel is programmed by con-
necting an external sense resistor RSENSE in series with
the LED load, and setting the voltage regulation threshold
across that sense resistor using CTRL input. If the CTRL
voltage, VCTRL, is less than 1V, the LED current is:
ILED
=
10
VCTRL
• RSENSE
www.DataSheet4U.com
If VCTRL is higher than 1V, the LED current is:
ILED
=
100mV
RSENSE
The CTRL pins should not be left open. The CTRL pin
can also be used in conjunction with a PTC thermistor to
provide overtemperature protection for the LED load as
shown in Figure 2.
VREF
2V
45k
50k
CTRL1-3
470Ω
PTC
3492 F02
Figure 2
Thermal Considerations
The LT3492 is rated to a maximum input voltage of 30V
for continuous operation, and 40V for nonrepetitive one
second transients. Careful attention must be paid to the
internal power dissipation of the LT3492 at higher input
voltages and higher switching frequencies/output voltage
to ensure that a junction temperature of 125°C is not
exceeded. This is especially important when operating
at high ambient temperatures. Consider driving VIN from
5V or higher to ensure the fastest switching edges, and
minimize one source of switching loss. The exposed
pad on the bottom of the package must be soldered to
a ground plane. This ground should then be connected
to an internal copper ground plane with thermal vias
placed directly under the package to spread out the heat
dissipated by the LT3492.
Board Layout
The high speed operation of the LT3492 demands careful
attention to board layout and component placement. The
exposed pad of the package is the only GND terminal of
the IC and is important for thermal management of the
IC. Therefore, it is crucial to achieve a good electrical and
thermal contact between the exposed pad and the ground
plane of the board. Also, in boost configuration, the
Schottky rectifier and the capacitor between GND and the
cathode of the Schottky are in the high frequency switching
path where current flow is discontinuous. These elements
should be placed so as to minimize the path between SW
and the GND of the IC. To reduce electromagnetic interfer-
ence (EMI), it is important to minimize the area of the SW
node. Use the GND plane under SW to minimize interplane
coupling to sensitive signals. To obtain good current
regulation accuracy and eliminate sources of channel to
channel coupling, the ISP and ISN inputs of each channel
of the LT3492 should be run as separate lines back to the
terminals of the sense resistor. Any resistance in series
with ISP and ISN inputs should be minimized. Avoid ex-
tensive routing of high impedance traces such as OVP and
VC. Make sure these sensitive signals are star coupled to
the GND under the IC rather than a GND where switching
currents are flowing. Finally, the bypass capacitor on the
VIN supply to the LT3492 should be placed as close as
possible to the VIN terminal of the device.
3492f
11
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet LT3492.PDF ] | |
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