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INA190: What is the REF input impedance?

Mark Major
Prodigy 65 points
Part Number: INA190

I have a bidirectional sensing application and am biasing the REF input at Vcc/2, in my case at 1.35V.

I am finding ~120 uA excess supply current draw and have so far traced it down to the reference signal.

This would amount to ~10k input impedance.  Could it be that low?  I'm not finding any specs for it in the data sheet.

The functional diagrams indicate its just a standard diff amp configuration but don't show the R value.

Does anyone know for certain the REF input impedance?

  • 0
    Prodigy 65 points

    Checking with a power supply and micro ammeter, it measures 14 uA at 1.35V indicating more like ~100k loading.  A complicating factor is the circuit has two INA190 chips in parallel, and both are being driven by the same Vref source.  One is disabled, the other enabled.

  • 0 in reply to Mark Major
    TI__Mastermind 29555 points

    Hey Mark,

    The REF impedance is RFB + Rint where RFB is 1MΩ. Here is the table of values for different variants, note it applies to the second stage of device.

    Device Rint nominal (kΩ) RFB nominal (kΩ)
    INA190A1 400 1000
    INA190A2 400 1000
    INA190A3 200 1000
    INA190A4 100 1000
    INA190A5 40 1000

    14 uA is still too high.

    Can I get a circuit PCB schematic as well as a testing schematic for your bench setup?

    Could I also get the part number for the ammeter used to make this measurement to confirm its accuracy at measuring 1µA?

    The two devices being powered in parallel should not matter, but I would try removing one and retesting separately to make sure that this is not a factor.

    Sincerely,

    Peter

  • 0 in reply to Peter Iliya
    Prodigy 65 points

    Great information, thank you!

    I'm going around in circles chasing the problem but I don't think its the INA190 input impedance based on your information and some other measurements I've done to isolate it.

    I believe the 14 uA is accurate using a Fluke 87 but the current must be going somewhere else.

    I'll write back if the problem has anything to do with nuances of using the INA190.

  • 0 in reply to Mark Major
    TI__Mastermind 29555 points

    Hey Mark,

    Let me know if I can look over any schematic or layouts to help. One thing to look out for are ground loops where the INA190 GND pin is not connected to system/board ground via a low-impedance trace.

    Sincerely,

    Peter

  • 0 in reply to Peter Iliya
    Prodigy 65 points

    Thanks, that would be great.  I can't just post my design to the forum, but if you have time for it then we could set up a video call and screen share the info.

  • +1 in reply to Mark Major
    TI__Mastermind 29555 points

    Of course. I can contact you in a private message with contact information.

    Best,

    Peter

  • 0 in reply to Peter Iliya
    TI__Mastermind 29555 points

    Hey Mark,

    Since I have not heard back from you after our call, I will mark this thread as resolved. However, if you have any other questions or updates please post back to this thread or create a new one.

    Sincerely,

    Peter