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Original question:

LM3643: Transfer efficiency

LM3643: is it constant current? Can I use it to drive Laser Diode?

Kelly Wang
Intellectual 550 points
Part Number: LM3643

LM3643 drives at constant current. May I use it to drive 3.7V to 5 V operating voltage laser diode?

  • 0
    TI__Mastermind 22745 points
    Hi kelly,
    Sure, we have some customer use this device to drive laser diode for facial recognization or barcode scanner. But there is a little question about the output volatge range, we have the minimum OVP voltage is about 4.75V, so could you make sure your forward voltage range. If it is less than 4.75V, it should be ok.
    Regards
    Sean
  • 0 in reply to Sean Zhou
    Intellectual 550 points

    Sean,

    Thank you for the reply. The laser diode has operating voltage range: 3.7V to 5.5V. I verified the operating voltage using a CC controlled power supply TP1803D. I tried to drive the laser diode, somehow, it can't turn on the laser diode. Currently, I configure LM3643 as the following,  other registers are in default value. Laser Diode connects to J3. Please let me know whether I need to modify any specific configuration to drive laser diode either in register or hardware.

    Register Address(hex)

    Register Data (hex)

    1

    25

    3

    		       25

     

      

  • 0 in reply to Kelly Wang
    TI__Mastermind 22745 points
    Hi Kelly,
    Yes, your configuration is right, but you need to pay attention to the maximum output voltage of LM3643 that I mentioned before, what's the maximum forward volatge for your laser diode at your maximum current? It can't support 5.5V.
    Regards
    Sean
  • 0 in reply to Sean Zhou
    Intellectual 550 points

    Sean,

    The laser diode was verified to be able to work at 3.7V, 300mA by using an DCpower supply module. So, the laser diode can work at 3.7V, which is less than 4.75V.

    Thanks,

    Kelly

  • 0 in reply to Kelly Wang
    TI__Mastermind 22745 points
    Hi Kelly,
    That should be ok for your application. Please help to click"Resolve", thanks.
    Regards
    Sean
  • 0 in reply to Sean Zhou
    Intellectual 550 points

    Sean,

    Somehow, your replies do not resolve the question I have. I will state my question in detail. Please let me know if you have any question on any unclear part.

    I have LM3643 design circuit PCBA(the circuit was posted in the post before). It drives LED perfectly. Now, I am considering using this LM3643 circuit to drive a laser diode. The diode has the following electrical spec:

    1.  Output Power: CW 1.6W
    2. Operating Voltage: 3.7-5.5V
    3. Threshold Current: 80mA

    4. Maximum forward current: 1.7A. 

    Somehow, the LM3643 circuit can't drive the laser diode.  I posted the LM3643 register configuration and circuit in the post before to consult what could be wrong with driving a laser diode.

    Thanks,