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LMG1020EVM-006: LMG1020EVM-006 problem, input J2

Li Tao13
Prodigy 50 points
Part Number: LMG1020EVM-006

I try to evaluate LMG1020EVM-006, but it did not work.

I wire bonded the anode of VCSEL to anode pads of EVM, and use silver epoxy to attach the bottom of VCSEL (cathode) to cathode pad of EVM.

I did the R10 and R3 rework to bypass the pulse shortener.

And I replaced the LDO with the new ones TI sent to me (with higher voltage setting).

 

I make sure the signal and ground are connected correctly.

I followed the steps on the user’s guide:

1, power up DC bias supply J1 at 5.5V, set current limit to 0.1A

2, connect function generator, set frequency to 100kHz, pulse width 100ns, signal at 3V, enable the output

3, power up input supply J2 at 10V, current limit at 0.1A (last time when I tested the old board,  the voltage on input power supply is ~1.8V with current limit at 0.1A.)

 

 

But there is still problem. When I turned on input supply J2, the power dropped to ~0.1V (set at 10V), it hits the current limit 0.1A.

 

The voltage between TP1 and PT3 GND is 5V.

BTW, I measured the resistance between the anode pad and cathode pad of my laser is ~1.2 Ohm, which is ok.

Could you help me?

Thanks!

Tao

  • 0
    TI__Genius 13445 points
    Hi Tao,

    Thanks for reaching out to us, someone will get back you soon to help resolve the problem.

    I appreciate your patience.

    Regards,

    -Mamadou
  • 0
    TI__Genius 12990 points

    Hi Tao,

    To properly bypass the pulse shortner (without using the AND gate as a buffer) and to drive 1020 input directly from the FG you have to do the R10/R3 rework as well as removing R9 rework to completely remove the pulse shortner and AND gate from the input. Can you confirm R9 is not populated and retest?

    Thanks,

  • 0 in reply to Jeffrey Mueller
    Prodigy 50 points

    Hi, Jeff,

    I removed R9. But it still does not work.

    What is your advice of next step?

    I think the difference of my test is from your other customers is that I try to bypass the pulse shortener circuit.

    I use HP8131A and a SMA connector on J3 to supply the pulse signal.

    Thanks,

    Tao

  • 0 in reply to Li Tao13
    TI__Genius 12990 points
    Hi Tao,

    Thanks for you update!
    Are you also trying to bypass the AND gate?
    I will get an new EVM and make the changes to bypass the pulse shortner/AND gate and apply the supplies and document everything to let you know my connections. If all the boards are behaving the same way its possible that its simply your connections that is the issue.
    I have also coordinated getting your broken EVM to myself so I can do a proper debug so I can be sure to return to you a working EVM.

    Thanks,
  • 0 in reply to Jeffrey Mueller
    TI__Genius 12990 points
    Hi Tao,

    update: I have taken this offline for the time being and will update this thread if the solution turns out to be a common problem/solution among 1020 EVM users. I suspect the reason why J2 VBUS output is hitting the current limit due to it being connected backwards. In this case the GAN would conduct current in the third quadrant and may cause damage.

    Thanks,