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LM3648: LM3648TT with Red Leds

fabio ortolano
Intellectual 330 points
Part Number: LM3648

Hello

I'm looking for a driver that handles up to 500mA for driving high power leds. I found this LM3648TT but my question is: could this driver be used also with RED leds?

Description of the project: I have to build up a matrix with 4 colors of led (white, blue, gree and red) and for each one I want to control the intensity (with currents up to 500mA each). I want to supply the system with 3.3V. On datasheets I only see the characteristics that starts from 2.5V for vout but for RED ones I need that the Vout ranges from 2.0 to 2.3V (I will use the XLamp® XQ-E LED Cree family). 

Thanks for the help

  • 0
    TI__Intellectual 1940 points

    Hello,

    Red LEDs can be driven with this part.  The only concern is thermal management.  With 3.3V in and an LED of 2V, @ 500mA of current the part will dissipate 650mW.  With a thetaJA of 90.2degC/W, you can expect a die temp rise of at least 58 degC over ambient.  This is assuming a JEDEC standard PCB which has a lot of copper.  If the PCB is not as large as the JEDEC form factor or has lower thermal performance, the die temp rise will be higher.  The max junction temp allowed for the LM3648 to stay within spec is 125degC.

    Hopefully this helps.

    Greg

  • 0 in reply to Greg Lubarsky
    Intellectual 330 points

    Hello Greg, thaks for reply. I understand the problem. So my question is: do you think it's better to regulate the voltage input to 2.8V in such a way there is a optimal trade-off between red and other color leds? If 'im right, the device have a switching boost so the power loss due to elevate the voltage is smaller that the power loss due to LDO when it needs to lower the voltage for RED leds. I didn't write that the input voltage is derived from 24V usingn an adjustable switching regulator, so I can set up the right voltage to minimize power loss (and of course rise of temperature).