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LMG1020EVM-006: what is the purpose of schottky diode in laser driver

veerababu ss
Prodigy 240 points
Part Number: LMG1020EVM-006
Other Parts Discussed in Thread: LMG1020

HELLO SIR,

i am using LMG1020  laser driver board, what is the purpose of schottky diode in laser driver 

  • 0
    TI__Genius 12990 points

    Hi Veerababu,

    Thanks for reaching out on e2e about LMG1020 EVM.

    The purpose of the schottky (D1 in the schematic) is to clamp the drain or cathode of the FET and laser so that the drain to source does not exceed limits as well as the reverse bias voltage of the laser. Since during turn off the laser peak current is still flowing, a voltage is induced across the common source inductance and overshoot also happens at the drain. A clamp can be used to protect the drain and cathode to the bus voltage however the placement, component selection and layout is all a trade off to achieving the best rise and fall times and performance of the laser. Please let me know if this helps answer your question. Check out TIDA-01753 below section 2.2.7 for more clamping diode details.

    Thanks,

  • 0 in reply to Jeffrey Mueller
    Prodigy 240 points

    thank you sir,

    i am using LMG1020 evm since 3 months,today suddenly GAN switching is not working and does not exceed specification 

    my observations are GANFET  cathode and gate are shorted(tested by using multi meter)

    can you tell what reasons for damage of GAN FET

  • 0 in reply to veerababu ss
    TI__Genius 12990 points

    Hi Veerababu,

    Sorry to hear about your issue with LMG1020 EVM. so your FET is short from drain to gate?

    have you removed the FET and used the DMM on the FET pads off the board to check the short?

    what conditions were you running the EVM in when the FET got damaged?

    are you able to replace the FET to see if that fixes the issue?

    Thanks,

  • 0 in reply to Jeffrey Mueller
    Prodigy 240 points

    thank you sir,

    i am trying to replace the GANFET, order was placed and waiting for new part

    i am operated at

    8 nS pulse width(generated by pulse shorten circuit @+IN)

    10 KHZ PRF

    LDO input 6V

    applied  high voltage 40V,

  • 0 in reply to veerababu ss
    TI__Genius 12990 points

    Hi Veerababu,

    Thanks for the update,

    Your operating conditions are within the capability of the EVM so I will have to see IN+, Vg and K waveforms to determine what the issue might be.

    Are you able to scope these waveforms after populating the new FET to see what the issue might be?

    I will mark the thread 'thinks as resolved' for now and you can repost to open back up the thread. Let me know if you have any other questions.

    Thanks,

  • 0 in reply to Jeffrey Mueller
    Prodigy 240 points

    thank you sir,

     i will update the waveform of +in,vg,k but it takes more than one week why because today i am ordered FET.

    if you have any information about cause of FET damage please update

  • 0 in reply to veerababu ss
    Prodigy 240 points

    hello sir,

    one more question about  selection of transimpedence amplifier(TIA)

    i am using APD for the purpose of laser range finding can you suggest suitable  TIA 

    my inputs are bandwidth 70-80MHZ,capacitance 4.4nF, dark current 10nA, responsivity 60A/W current from APD 10s of  nA 100s of nA range

  • 0 in reply to veerababu ss
    TI__Guru**** 189401 points

    Hi, 

    Unfortunately, a different group supports our TIAs. Can you post a new thread asking for help on them?