LT3496 LINER [Linear Technology], LT3496 Datasheet - Page 12

• Manufacturer Part Number: LT3496
• Description: Triple Output LED Driver
• Manufacturer: LINER [Linear Technology]

LT3496
Programming the LED Current
The LED current of each channel is programmed by con-
necting an external sense resistor R
the LED load, and setting the voltage regulation threshold
across that sense resistor using CTRL input. If the CTRL
voltage, V
If V
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.
Thermal Considerations
The LT3496 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 LT3496 at higher input
APPLICATIONS INFORMATION
12
I
I
LED
CTRL
LED
=
=
is higher than 1V, the LED current is:
10 • R
R
100mV
CTRL
SENSE
V
V
REF
CTRL
, is less than 1V, the LED current is:
SENSE
45k
5k
PTC
2V
Figure 2
3496 F02
50k
SENSE
CTRL1-3
in series with
voltages to ensure that a junction temperature of 125°C
is not exceeded. This is especially important when operat-
ing at high ambient temperatures. 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 LT3496.
Board Layout
The high speed operation of the LT3496 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 confi guration, the
Schottky rectifi er and the capacitor between GND and the
cathode of the Schottky are in the high frequency switching
path where current fl ow is discontinuous. These elements
should be placed so as to minimize the path between
SW and the GND of the IC. To reduce electromagnetic
interference (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 chan-
nel to channel coupling, the CAP and LED inputs of each
channel of the LT3496 should be run as separate lines
back to the terminals of the sense resistor. Any resistance
in series with CAP and LED inputs should be minimized.
Finally, the bypass capacitor on the V
LT3496 should be placed as close as possible to the V
terminal of the device.
IN
supply to the
3496fe
IN