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Original question:

LMG1020: Help with eval board

LMG1020: Output current drawn to low

Abel Martin
Prodigy 60 points
Part Number: LMG1020

Tool/software:

Dear TI,

I am using LMG1020 EVAL KIT to drive a laser diode capable of 15W optical power.

  • Diode Laser voltage 13V-20V
  • Current up to 5A 
  • Signal generator connected directly to IN+, Pulse waveform 20ns, 50Khz frequency, Duty cycle 0.1%

I want to get the total power from the diode and I cannot change the duty cycle because this will damage the diode in the end, the actual current is <1mA at 0.1% , all the signals are looking fine : gate,K, IN+, but the current is very low.

Please support!

Regards,

Abel

  • 0
    TI__Expert 7610 points

    Hello Abel,

    The diode laser voltage supply needs to be current limited to achieve maximum power from the diode without damaging it.

    The output gate resistance of the gate driver can also be increased to slow down the output slew rate and limit high peak current transients.

    This document has a detailed design explanation.

    https://www.ti.com/lit/an/slla456/slla456.pdf

    Thanks,

    Walter

  • 0 in reply to Walter Zollinger
    Prodigy 60 points

    Hello Walter,

    Thanks for your answer.

    You are referring to the R1,R2 resistors ? I am using the EVM and the laser diode is soldered directly to the pads, I cannot drawn more than 1mA from the external power supply connected to the J2 connector, only if I change the duty cycle. 
    How can I test that the circuit is working ( without the diode connected) ?

    Thanks,

    Abel

  • 0 in reply to Abel Martin
    TI__Expert 7610 points

    Hello Abel,

    Yes R1 and R2 on the EVM can be used to control the turn on and off time. 

    The circuit can be tested without the diode connected by adding resistors to R5-R8 to simulate the diode load. The circuit can be tested and the timing and current can be adjusted with the resistors in place. Remember to remove the resistors before adding the laser diode. There is more information on this in the EVM user guide.

    Thanks,

    Walter