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LMG1025-Q1EVM: Driving laser diode

Gerald
Genius 9575 points
Part Number: LMG1025-Q1EVM

Hi Experts,

May I ask for help? Our customer have a concern as shown below:

"I'm looking at the specs of LMG1025-Q1EVM. Some of it does not make sense. The Vbus current is limited to 0.2 A & 75 V; However and FET chip supports CW current up to 18 A and pulsed up to 75 A. How one can drive a lader diode with 0.2 A? It says that, in principle, pulse 40 A are possible. I wonder how I can creaete 40--75 A pulses if Vbus is current limited to 0.2A? I need to now real specs limitations given maximum current vs. pulse length. You should check the specs of EPC2212 that is used in your board. It seems your board provides very limited test options. FET permits a lot more."

I hope you can help us. Thank you.

Kind regards,
Gerald

  • 0
    TI__Genius 9301 points

    Hi Gerald, 

    Thanks for reaching out to us. I wasn't able to get a clear answer from the available documentation so I've reached out to one of our experts on this EVM and will provide an update by today.

    Best regards,

    Leslie

  • 0 in reply to Leslie Marquez
    TI__Genius 9575 points

    Hi Leslie,

    Thank you for your response. I will be waiting for your updates. 

    Kind regards,
    Gerald

  • +1 in reply to Gerald
    TI__Genius 9301 points

    Hi Gerald,

    The 0.2-A is an example for the current limit on the bus line. The board is actually limited to 2-A due to rating of the Schottky diode D1 on the Vbus line. The board could support higher current with the adequate components ratings.  

    With higher input current, they may need to update R5,6,7,8 resistors (if being used) to accommodate the increased power dissipation.

    Best regards,

    Leslie

  • 0 in reply to Leslie Marquez
    TI__Genius 9575 points

    Hi Leslie,

    I am sorry for re-opening the case status but I received a feedback from our customer.

    Please see below:
    "I believe you are mistaken. First, D1 is added to reduce possible oscillations (given a non-zero inductance, which is a standard practice, you may google " inductive kickback" ), there is very little current through D1 (check the polarity); Second, it is mentioned in the TI manual that 40 A is possible in a pulsed mode, but no details are given."

    I hope to we can further received your advise. Thank you so much in advance.

    Kind regards,
    Gerald

  • +1 in reply to Gerald
    TI__Genius 9301 points

    Hi Gerald, 

    Thanks for the feedback. Please let customer know that as long as the ratings of the board components are not exceeded they should have no problem with the board handing the FET's pulsed current spec.

    Regards,

    Leslie