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LMG1020: Output Current, Data rates

Rocky Isa
Prodigy 150 points
Part Number: LMG1020
Other Parts Discussed in Thread: ONET1151L

I have a couple questions relating to the data sheet:

1. I do not see anything about data rates, usually other drivers i have seen can go up to 32 Gbps. My equipment at my university and only handle a max of 1 Gbps. I would like to know the range of the data rates.

2. My project will need to be low power, and in making sure it does not take too much power, we need to drive a laser diode that operates within 20 mA. Ive noticed the peak output current is at 7 Amps. Can that be adjusted to a lower amount? if so, what is the range it can be adjusted to. Thank you.

  • 0
    TI__Intellectual 805 points
    Hello Rocky,
    LMG1020 is a low side GaN driver with 1ns min pulse-width and 375ps typical rise time charging into a 100pF load. It is intended to drive a power GaN FET; therefore, datasheet parameters reflect the times required to charge and discharge a power FET.

    Gate drive currents typically reflect the pull-up and pull-down resistances of the totem-pole driver inside and indicates the power dissipation inside the driver. When we drive a FET with any driver, the current is typically limited by the gate resistor.

    I believe you are trying to directly drive a 20mA laser diode directly with this driver. Can you send us a simple schematic so that we can better understand your application?

    Regards,
    Serkan
  • 0 in reply to Serkan Dusmez
    Prodigy 150 points

    Well we Haven't gotten to the design phase. We are trying to create a LiDAR application that measures the distance of an obstructing object. We are trying to find a laser driver to drive the laser diode, so yes, we are trying to directly drive a laser diode directly. For instance, we want to drive the follow laser, HFE6192-761. We want this to then be pulsed and create a pulse width of under 5 ns. Our product needs to be efficient so we need to find a laser driver with low output current. This is the general schematic that would be implemented

  • 0 in reply to Rocky Isa
    TI__Intellectual 805 points
    Thanks for the application schematics. The totem-pole driver inside LMG1020 is meant to drive a GaN FET; thus FETs inside the driver are too large for this application. The maximum switching frequency is limited to 60 MHz due to thermal constraints. Therefore, it is not possible to get 1 Gbps with LMG1020. This driver is not optimized to directly drive a laser diode. It would only be viable solution if you switch less than 60 MHz.

    Serkan
  • 0 in reply to Serkan Dusmez
    Prodigy 150 points
    Are their any laser drivers that can be used for outputting low current for our application? On top of that, I dont think we would need switching frequency to be higher than 60 MHz. Most other applications i have noticed are well under 60 MHz.
  • 0 in reply to Rocky Isa
    TI__Intellectual 805 points
    Something like ONET1151L seems more suitable for your application. I recommend that you open up another thread for this part to reach to relevant experts.

    Regards,
    Serkan
  • 0 in reply to Serkan Dusmez
    Prodigy 150 points
    What if we did not directly connect it to the laser diode? is there a way to input a MOSFET in between to lower the current?
  • 0 in reply to Rocky Isa
    TI__Prodigy 645 points
    A simple resistor in series should limit the current. It looks like that diode as a ~2V foward drop, so with a 5V supply 3V would develop across the resistor. So if you want 20 mA current, 3/20mA=150 Ohms in series with the laser diode directly connected to the LMG1020 output should do what you need.

    Also, to clarify Serkan's comment above, 60 MHz is not a hard limit, the limit is thermal. You can switch it faster if you respect the thermal limitations. (i.e. sending bursts of 200 MHz pulses could be fine)

    Regards,
    Nathan
  • 0 in reply to Nathan Schemm
    Prodigy 150 points
    so it is possible to drive a laser diode directly? is their any drawbacks from simply placing a resistor in series?
  • 0 in reply to Rocky Isa
    TI__Prodigy 645 points
    The current will have some variation due to the variation of the forward voltage of the laser diode. Other than that, it should work fine.