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INA302: Adding delay to the both comparators

Eraj Yunus
Prodigy 11 points

Part Number: INA302

Hello Team,

I am using the INA302 to protect a 28V 15A power supply's output. I have the individual comparators to set two trip points, 13A and 15A. The 13A trip is tied to the second comparator and has a 2.5ms delay thru pin10 using a capacitor, and is working well. The 15A trip is tied to the first comparator. However, the 15A trip keeps happening when the power supply load changes. The switching transients can be higher than 15A and last about 2-3ms. I was wondering if there is a way to add a delay to the first comparator so it would stop tripping on load changes, because the default is <1us? If not is there a way to filter out the transients so the 15A doesn't trip on load changes?

My schematic is identical to the datasheet example fig. 48, with 7.5R input terminal resistors.

Thanks,

Eraj

  • 0
    TI__Mastermind 20170 points

    Hi Eraj,

    Thank you for your post. Let me look into this and give you feedback no later than the EOD Tuesday (4/30).

    Thank you for your patience,

    Joe

  • 0 in reply to Joe Vanacore
    TI__Mastermind 20170 points

    Hi Eraj, 

    Thank you for your patience. 

    Implementing an input filer for the INA302 would be a good option and I believe this is your current approach:

    This is an equation from another datasheet but using this filter would allow you to size the resistors and caps to the appropriate frequency to avoid the transients from being seen at the outputs. Have you tried resizing the differential cap to decrease the 3db cuttoff frequency?

    Just in case you haven't performed the error calculations, I have provided them below:

    This paired with increasing the size of the pull-up for the comparator with the 15A threshold would be a great approach. 

    I hope this helps. 

    Best Regards, 

    Joe 

  • 0 in reply to Joe Vanacore
    Prodigy 11 points

    Hello Joe,

    Thanks for the filtering information, I think that is exactly what I was looking for. Do you know if there are any limits to the Input Capacitor (Cf) size? I am thinking of using 47uF. Along with 7.5R series resistors, should get a 225Hz 3dB point. 

  • +1 in reply to Eraj Yunus
    TI__Mastermind 20170 points

    Hi Eraj,

    I am happy this helps and I hope it works out. 

    There is no limit to the CF and 47uF should be good with the 7.5 Ohm resistors. 

    After you do the error calculations, make sure that it is reasonable for your system. 

    If not, I would recommend a low pass at the outputs. 

    Best Regards, 

    Joe

  • 0
    Prodigy 11 points

    Hello Joe,

    I increased the input capacitance to 47uF and the transient noise is filtered out. No longer getting false trips. Thanks so much!