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LMG1020EVM-006: current sensing with GaN

K.Hamamoto
Guru 12155 points
Part Number: LMG1020EVM-006
Other Parts Discussed in Thread: LMG1020

hi

I am considering to evaluate with combined LMG1020EVM and Laser diode. However we are concerned how to measure the peak current flows GaN.

I read the following document (application note).

http://www.ti.com/lit/ug/tidue52/tidue52.pdf

At P.13-19 on the following application note, it mentioned there are no method to measure the current directly.

(Before checking this application note,we were considering to add the cement resistor into GND line for current sensing.)

On the other hand, there are two method indirectly as mentioned bellow.

1)Create a model to include the parasitic inductance of the components, connections, and PCB traces.

2)Measure the power from the from the light pulses generated by the laser.

Therefore,I have a question. There are no explanation on the application note about the method of 1). How can we measure the current by creating that model?

Best Regards,

Koji Hamamoto

  • 0
    TI__Guru**** 189401 points
    Hi Hamamoto-san,

    Basically, you model all the parasitic elements in your circuit, and using a circuit simulator, you could then determine the current going thru the laser diode.
  • 0 in reply to Don Dapkus
    Guru 12155 points
    Hi Don-san,

    Thank you for your reply.

    I understand. The method is not actual result. It is only calculated by simulator.

    So in other words, is it only one method can measure for the actual current? (by measuring the light power with a equipment)

    As I mentioned at above post, we were considering the current sensing by sense resistor. I understand the peak current is large and fast.
    And we were considering a cement resistor for it and were going to measure the voltage change between that.

    Do you think the method is not good for this measurement?
    (Ultimately, we will measure by the equipment such as light power meter or optical detector . But that kind of the equipment is expensive.)

    Could you give us any advice the way to measure the peak current easily(not need high accuracy.)?

    Best Regards,
    Koji Hamamoto
  • 0 in reply to K.Hamamoto
    TI__Genius 12990 points

    Hi Koji-san,

    Im an apps engineer working with Don on this device and hope to help. Using a current sense resistor may introduce so much inductance it will prevent the current from reaching its peak.

    To find the peak current for your laser pulse you need a calibrated instrument such as Thorlabs PDA150A to extrapolate the peak current through the laser by measuring the peak power of the optical pulse (measured by a PIN or APD). Typically manufacturers provide an optical output vs current graph. If you can capture the light peak power this equates directly to an instantaneous current. The 1020 TIDA page 12 gives an example to follow:

     let me know if you have any more questions!

    thanks,

  • 0 in reply to Jeffrey Mueller
    Guru 12155 points
    Hi Jeff-san,

    I appreciate kind your support.
    We are planning to get the photo detector anyway. So,I hope you will be able to help me if I should encounter any problems.

    Best Regards,
    Koji Hamamoto
  • 0 in reply to K.Hamamoto
    TI__Genius 12990 points
    Hi Koji-san,

    I will help you the entire way. Any problems pop up just reach out. Feel free to let me know your feedback or your success and hardships using LMG1020 for driving laser pulses.

    thanks,