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LM5069: PWR resistor

Kevin Hua
Prodigy 30 points
Part Number: LM5069

Tool/software:

The controller has a Power Limit functionality that connects to the PWR PIN. Adjusting the resistor value allows to set the power limit on the Pass-FET by modulating the Gate-to-Source voltage of the FET. During simulation, adjusting this resistor did not seem to limit and modulate the Pass-FET. By design, I needed to set the resistor to 45k and expect a power limit of 75W. I adjust this resister all the way down to 100 ohms and all the way up to 500k ohms and saw no change in the results for the power at turn on. My team suspects that there is a time limitation to how fast the controller is able to process the power before limiting it. I will add a screen shot of the simulation to give you a time base. Please advise.

Thanks,

Kevin Hua

  • 0
    TI__Guru* 79181 points

    Hi Kevin,

    Please share test schematic.

    Regards 

    Kunal Goel

  • 0
    Prodigy 30 points

    Hi Kunal,

    Due to ITAR requirements, I am unable to share the schematic I am using. The basics of the schematic is an input of 32V, Rsense of 5 m ohms, and Rpwr of 45k ohms. I am more curious about the bandwidth of the gate control of the power limiting circuit shown in the functional block diagram. I want to know if the short spurt of power spike is too short to be processed by the gate control.

    Thanks,

    Kevin Hua

  • 0 in reply to Kevin Hua
    TI__Guru** 105561 points

    Hi Kevin,

    Are you changing Rpwr on the fly ? 

    Power limit response time is in the order of 50 us.

    What is the load during your simulation ? We need your sim file to run and check the issue.

    BR,

    Rakesh