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INA233: scale current sense signal

HKH
Prodigy 105 points
Part Number: INA233


Hi,

I need to measure a DC current of max. 1A (during startup) and 100mA nominal. The absolute accuracy is not critical, only the relative precision at nominal current.

In order to be able to measure the full range though, I need 15uA resolution and also I need maximum 0,5 mA drift over a temperature swing of max. -10/+35 °C from 25 °C at nominal current (100 mA).

Hence I need maximum 15 PPM resistor and < 80 mOhm, due to full scale is ~ +/-80mV shunt voltage with INA233.

There are not many resistors to choose from in low ohmic chip resistors with low TCR.

Could I choose eg. 100mOhm for current sensing and divide that using 1k+3k3?

  • 0
    TI__Mastermind 26335 points

    Hello HKH,

    Thank you for considering to used Texas Instruments in your design.  You could do that, but then you will have potentially a large error in your measurement.  Below I illustrate the impact of your divider on various sources of error.    With 1% tolerance resistors you could get measurements similar to the bottom left.  Even with perfectly matched resistors for your divider, these are in parallel with the internal differential impedance of the device (around 5k for each input).   The influence of the internal impedance on the divider can be seen in the top right.  Then there is the effect  of offset produced by the device's input bias current seen in the bottom right.

    Consequently you may want to consider using a lower shunt resistor that satisfies your PPM requirement and does not have a substantial lead time or inflated cost.  From what I see on digikey, you may be able to use a 50mohm.  Or you may consider putting a 200m and 100m in parallel to get a resistance of 66mohm.