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Original question:

INA180: INA180 high end current sensing

INA180: INA180

Ranjeet Malhotra
Prodigy 85 points
Part Number: INA180
Other Parts Discussed in Thread: MSPM0G1505,

Tool/software:

Hi,

Can the output of the INA180A1 be directly connected to one of the A/D channels of MSPM0G1505 inputs to read the current?

The Microcontroller A/D input resistance is about 0.5 K ohm based on the datasheet based on Section 7.12.1 of the datasheet.

thanks

  • 0
    Guru 298810 points

    See figure 7-19 for what output currents are supported.

    But the ADC's sample-and-hold capacitance is 3.3 pF, so even a much smaller current limit would not matter.

  • 0
    TI__Expert 3905 points

    Hi Ranjeet,

    In short, yes you can connect the INA180 directly to the A/D channels of the microcontroller given there is sufficient sampling time. To find the sampling time, you can do one of the following:
    (i)  Use the equations listed in the MSPM0G1505 datasheet to calculate the minimum sampling rate.

    (ii) If you don't have all the variables to calculate time using the equations above, you can use the GPAMP electrical characteristics and set minimum sampling time to 3 us. (The INA has better slew rate and BW compared to the GPAMP, so 3 us shouldn't give you much error.) 

    In conclusion, this would work, please keep in mind that there maybe output load stability issues, the following app note details this for your reference.
    https://www.ti.com/lit/an/sboa443/sboa443.pdf

    Also, you can reduce the settling error by maximizing your conversion time, but this will lead to some loss in bandwidth.

    If you have any further questions, please feel free to reach out.

    Best,
    Mallika Senthil

  • 0 in reply to Mallika Senthil
    Prodigy 85 points

    Thanks for the comments - we used a Rpar of 100 ohm; Cpar of 0.1uF; sampling time is set to 125 uS. Hardware averaging is enabled to 128 samples.

    When we measure the output from the Micro - we see a variation in measured values. The input to the ADC is measured on a scope/multimeter and it is noise free. I suspect that the sampling is not set  properly. Is it possible to get some feedback on likely cause.

    thanks

    regards, 

  • 0 in reply to Ranjeet Malhotra
    TI__Expert 3905 points

    Hi Ranjeet,

    Yes, I think the sampling time is too large. Try something between 3 us and 40 us and see if the output changes. If not, please attach your scope shots here.

    Best,
    Mallika Senthil

  • 0 in reply to Mallika Senthil
    Prodigy 85 points

    Hi Mallika, 

    Can I send the schematics/waveforms directly - I cannot share the same in a forum.

    thanks

    regards, 

  • 0 in reply to Ranjeet Malhotra
    TI__Expert 3905 points

    Hi Ranjeet,

    Yes, sure.

    Best,
    Mallika Senthil

  • 0 in reply to Mallika Senthil
    Prodigy 85 points

    is there an email address I can send the information to?

  • 0 in reply to Ranjeet Malhotra
    TI__Expert 3905 points

    Hi Ranjeet,

    This is a public forum and I can't disclose my email here, you can directly inbox the scope shots to me on this E2E platform. I've sent you a friend request on E2E, please accept it and then send the scope shots via direct message.

    Best,
    Mallika Senthil