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Issue with INA333

sushruta shetty
Prodigy 100 points
Other Parts Discussed in Thread: INA333, INA188, INA326, INA213

Hi

We are using INA333 in our new design for current sensing application. Schematics snapshot is attached for your kind perusal.

INA333AIDGKR is the full part no for the device.

We are able to observe 54mV at the differential inputs of the device, But we are not able to observe any significant voltage at the output. When observed across Vref and Vout pin, we are able to observe only 0.2mV. Is this because of high common-mode voltage?

Awaiting your reply.

Thanks and Regards

Sushruta 

  • 0
    TI__Mastermind 25865 points
    Hello Sushruta,

    There are 2 issues going on here:

    1) The common-mode voltage of the shunt resistor appears to be 5V, which is the same as the supply voltage of the INA333. This is not in the linear operating region of the INA333. Please read the following FAQ:

    e2e.ti.com/.../3373.understanding-instrumentation-amplifier-vcm-vs-vout-plots

    2) The reference pin is not connected to a low-impedance source. You should buffer the reference voltage with an op amp. Please refer to section 8.2.2.3 in the INA333 data sheet.

    Here are a few recommendations:

    1) Switch to a device like the INA188, but you will have to power the device using the 24V source. Note you will still have to buffer the reference pin.

    2) Alternately you could switch to the INA326, which is a 5V device. The INA326 has a unique topology that requires 2 gain setting resistors. Please note that it is low-bandwidth and make sure there is minimal stray capacitance on the gain setting pins. It is the only device in our portfolio that I'm aware of that does not require a buffer for the reference voltage. In the end this may be your best instrumentation amplifier option.

    3) Finally, you could consider using a current shunt monitor (e.g. INA213). These devices have a fixed gain, so it's likely that you will need to select a different shunt resistor. If this interests you I can move this post to the Current Sensing Forum for help selecting the right device.