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LM3560 - Torch Mode Question

Eric Hackett
Guru 74322 points
Other Parts Discussed in Thread: LM3560, LM3424

Hello everyone,

I have some questions regarding the LM3560.

  1. What is limiting the torch mode to 250mA (software, switch, temperature)? Is there a way to drive it past 250mA in a continuous mode?
  2. This part is made for driving two LEDs off of a LI ion battery. Is there another TI part that is similarly integrated that can drive 4-6 high current LEDs in some configuration?

From what I've read in the datasheet, it seems like the limit is preprogrammed into the chip, and I don't believe there is a way to drive it past 250mA, but I wanted to run it by some people more experienced with the part. Same with the second question, I couldn't find anything, but I wanted to ask someone who knows a lot more about this product line before I stopped looking.

Any and all help is greatly appreciated.

Thanks,

Eric

 

  • 0
    TI__Intellectual 1040 points

    Eric,

    The torch current is internally set to 250mA max per current source (500mA total).  You can use the flash current settings which are up to 2A, but you will need to work around the internal timeout counter.  This timeout counter can be set from 32ms up to 1024ms and if it expires,will turn off the device.  If you set it to 1024ms then control the LEDs with the STROBE input,you can periodically pulse the STROBE pin low for > 10us which will reset the internal timeout counter.  Pulsing it low for 10us - 100us will be outside the repswonse time of the boost circuit so the LEDs will remain on constantly.  This will basically force the timeout and STROBE input to act like a watch dog timer.  As long as the STROBE pulse period is less than the programmed timeout counter the LEDs will stay on continuously at the programmed flash current.  This is the only way to get constant currents > 250mA per source.

    Another device we have that uses an external FET and can drive multiple series LEDs is the LM3424.  The VIN range might not go low enough for single cell Li+, but if you have a 5V source you can power VIN from that and drive the input of the inductor with the Li+ voltage.

    Thanks

    Travis

  • 0 in reply to Travis Eichhorn
    TI__Guru 74322 points

    Travis,

    Thank you very much for the thorough response, I appreciate it. If I have any more issues with this part I'll post them in this thread.

    Regards,

    Eric