LT3496(RevE) View Datasheet(PDF) - Linear Technology

Part Name

Description

MFG CO.

LT3496
(Rev.:RevE)

Triple Output LED Driver

Linear Technology 

LT3496

APPLICATIONS INFORMATION

Programming the LED Current

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

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.

2V

VREF

45k

50k

CTRL1-3

5k

PTC

3496 F02

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

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 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

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 VIN supply to the

LT3496 should be placed as close as possible to the VIN

terminal of the device.

3496fe

12

Share Link: