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INA149: question of INA149

Zhonghui Xu
Expert 5445 points
Part Number: INA149

HI TEAM,

I got questions from customer.

In Data sheet of INA149 , page 17 , It's written that the error is around 1.6% for 1V full scale.
but for specific shunt resistor and Current value of 1 ohm and 1 Ampere.
if I changed both of them to keep the full scale always 1V will the error be constant even at low current ranges ?

I have 2 more points that I need confirmation on regarding the device , is it bidirectional and does it work on both high side and low side ?

That's all thank you very much.

best regards,

  • 0
    TI__Guru 62700 points

    Zhonghui,

    Below please find the answers:

    If you change Rs 1ohm and 1A current but your full scale voltage remains 1V, 1.6% maximum error will hold for as long as the value of Rs is 5ohm or less.  Otherwise, you must match Rs with addition of Rc to minimize CMRR error (see below).

    Additionally, if Rs is greater than 50ohm, the Gain error becomes greater than 0.02%.  Thus, in order to mitigate the error, you must slightly increase Rs to Rs' (see below).

    Rs'=Rs*[380k/(380k-Rs)]

    Keep in mind that the dominant error in the Error Budget calculations shown below comes from CMRR - if you use the dual supply voltage (e.g. +/-15V) with Vcm at mid-supply (ground), this error gets eliminated as it is already included in the offset voltage. 

    As far as your question regarding whether the device is bi-directional and does it work on both high side and low side, it all depends.

    If you use dual supply with Vref=0, the answer is yes to both of your questions - see below.

    However, if you use a single supply, the answer is yes ONLY if you use Vref at mid-supply (e.g. Vref=2.5V for Vs=5V) - see below.