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INA290: Measure current from 0.01A to 200A

Part Number: INA290
Other Parts Discussed in Thread: INA228, INA229,

Hi Team,

This inquiry is related to the other thread below. Our customer would like to confirm if the INA290 can be used to measure current from 0.01A up to 200A. He will then connect the output to a 16-bit or 20-bit ADC. 

https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/1070951/ina226-current-monitor-of-0-200a-with-0-01a-resolution 

With a current sense resistor of 0.4096 mohm, the voltage drop @ 0.01A would be 4.096uV. However, the offset voltage of INA290 is +/-12uV which is higher than the voltage drop of the resistor, hence, it can't accurately measure a current of 0.01A. Can you please confirm if my understanding is correct? Can INA290 measure current from 0.01A up to 200A?

Regards,

Danilo

  • Hello,

    Yes you are correct in saying that with the 0.4096 mohm Rshunt the INA290 would not be able to accurately measure 0.01A. The INA290 will not be able to measure from 0.01A to 200A as either the bottom range will suffer due to accuracy or the top end will suffer due to power constraints. Picking a bigger Rshunt will help the accuracy near 0.01A but you will run into power limitations of the resistor near the 200A. 

    In the post you linked Mitch suggests the INA228/INA229, those will be the best performing part for the dynamic range you are looking for. 

    Regards,

    Castrense

  • Hi Castrense,

    Thank you for the confirmation.

    Currently, our current/voltage/power monitor devices such as INA228 and INA229 are out of stocks. I have searched our current sense amplifier if we have one that can measure between 0.01A to 200A, however, most devices doesn't meet this requirement. Do we have an alternative solution?

    Regards,

    Danilo

  • Hello,

    With the Rshunt you have selected it will be very difficult to get the low accuracy. If you can share the customer application maybe we can think of an alternative solution. Either here or through email.

    Regards,

    Castrense Nigrelli

  • Hi Castrense,

    Here is the customer's feedback regarding their application. 

    1. Please refer to the attached figure for the application diagram.



    2. The load you want to measure is special equipment (PCB plating equipment).

    3. If you change the measurement current to 0.1A, is it possible to measure with INA290? I plan to use INA290 and GAIN 200.

    4. Current sense amplifier error analysis INA290-Q1 from homepage is calculated up to 100A, is it not possible to use up to 200A with this part?



    5. When using this part, 0.01A cannot be measured. Is it possible to measure 1.001A or 10.001A?

    Regards,

    Danilo

  • Hello,

    I will work with these values: Gain = 200V/V, INA290, Rshunt = .4096mohm.

    The lowest possible current we can measure without hitting the swing low limit (.025V Max swing low limit) would be .305A. This would be with an error of ~10% just from Vos.

    If with this same setup you are wanting to measure 200A, Vout = 16.38V (ideal), so you will need to supply the INA with about 16.6V to satisfy the max swing high limit.

    Yes, the INA290 can measure 200A as long as the circuit is designed properly and keeps the INA in the linear region.

    If we use the INA290 error calculator on the product page we can see that at 1A we will get ~2.29% resulting in .0229A error. At 10 A we get an error of ~.39% resulting in .039A. 

    Regards,

    Castrense

  • Hello.
    Please share your development again and review if my calculations are correct.
    1. Current measurement: 0.1~200A , Rshunt: Use 0.1mohm
    2, calculation details
    According to my calculations, if it is greater than 0.3A, all other currents are measurable. (This is the most important question.)

    INA290
    VOS       GAIN VOUT
    0.000025 200   0.005

    Isense Rshunt GAIN VOUT
    0.1         0.0001 200 0.002 not measured
    0.2         0.0001 200 0.004 not measured
    0.3         0.0001 200 0.006 not measured or measurable
    0.4         0.0001 200 0.008 measurable
    0.5         0.0001 200 0.01 measurable

    1            0.0001 200 0.02 measurable
    1.01       0.0001 200 0.0202 measurable
    1.02       0.0001 200 0.0204 measurable

    10          0.0001 200 0.2 measurable
    10.01     0.0001 200 0.2002 measurable
    10.02     0.0001 200 0.2004 measurable

    200        0.0001 200 4 measurable

  • Hello,

    You are calculating the Vout correctly but swing low is Vout > 0.005V for typical INA290s or Vout > .025V for worst case INA290s.

    We must now decide if we want to calculate values based on typical specifications or max specifications. 

    If we use Rshunt = 0.1mohm, using the typical Vout swing low spec the smallest measurable current = .25A. If we use the max Vout swing low spec the smallest measurable current = 1.25A. 

    The next question is what can we measure. The linear range of the INA290A4 with Rshunt = 0.1mohm will be from (using typical values) .005V > Vout > Vs - .07V, if Vs = 5V then .005V > Vout > 4.93V. 

    The ideal measurable current range is .25A > Current > 246.5A. 

    I think the question you are trying to ask is what is the smallest step in current we can measure? I believe the percent error of the INA will give you the smallest step in current you can measure.  Meaning if I am trying to measure 1A and have a percent error of 12% and we are certain that the current going through the shunt is 1A the output of the device (without the shunt resistor error) can be any value between .88A to 1.12A. I got the percent error from the INA290 product page error calculator. It is good to know that the product page error calculator uses worst case errors in a RSS formula.

    What is the accuracy you are targeting at the low end of the current measurement?

    Regards,

    Castrense