(AD8417)If I can calibrate the system , can I cancel the input offset?


Hi !

I have few questions about AD8417.

I am suggesting AD8417 to one of my customer to sense the current of the battery system with high side.

The system which I suggest now is this.

And the competitor is INA213-Q1(http://www.tij.co.jp/jp/lit/ds/symlink/ina213-q1.pdf ).

To reduce the offset and gain error, I am suggesting to calibrate the system.

1)

If our customer calibrate the system with 0A , can they cancel VOLTAGE OFFSET(RTI)?

And if they can do this, will it be only temp drift to take care about with the system after the calibrate?

2)

Our customer wants to sense 0A exactly.

But every AMP cannot output 0V.

So I am suggesting to shift the common level more than 0.5V to sense 0A and calibrate the system.

Is there other way to sense 0A and also keep the wide range output as possible as they can?

3)

The system supply voltage is 12V so 70V common level is too much.

Also they don't need high frequency as AD8417 has.

I think input offset will be calibrated so it will be canceled.

The most important spec is temp drift .

Can you give me some other advise to win to INA213-Q1?

Best regards.

Kawa

  • Hi !

    Can anybody give me any advice about this?

    Best regards.

    Kawa

  • Hello Kawa,

    If you have a way to disconnect the high end of your resistor from the source (maybe a switch), then it does look like you could calibrate that error our correctly. What you get out of the ADC in that condition should be the error that you want to calibrate out. It also looks like you have the right idea going for the largest dynamic range at the output, by shifting the output using the reference pins to just above the minimum voltage the AD8417 can output.

    There are current sense amplifiers that may be a bit more loose in terms of common mode voltage range and bandwidth, such as the AD8209, but that would have higher drift compared to the AD8417. In your case where you want to go for very low offfset drift and gain error, it does look like the AD8417 is overall a good choice.

    I will check this out with our other engineers and get back to you if I can with more input.

    Thanks,

    Kris

  • Hi Kris!

    Thank you for your answer and support.

    I understood what you wrote.

    I think for the current sense AMP , AD8417 is best for our customer.

    But now they are thinking to use Diff-ADC.

    => The competitor is INA226-Q1 or INA220-Q1.

    http://www.tij.co.jp/jp/lit/ds/symlink/ina226-q1.pdf

    The reason of this because to sense current with more high accuracy,

    they need high performance Current Sense AMP + ADC + Ref(ex ADR3540).

    This will be expensive for our customer.

    So maybe I gona change my proposal to AD7357 from current sense amp.

    But with the Web-Price I think it will be tough.

    Best regards.

    Kawa