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INA193: Accuracy

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Replies: 5

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Part Number: INA193

I'm using INA193.

I hope to know about output voltage accuracy.

1. In the spec.sheet, There are many word "VS".
   VS is meaning V+ in my understunding.
   But there are word V+ and also Vsupply.
  
   At 8.4.2.3,   Low VSENCE Case 1:VSENCE<20mV,-16V<VCM<0;
   and Low VSENCE Case 3: VSENCE<20mV , VS<VCM<80V
  
   In this sentence Case 3, Is it meaning VSENCE<20mV , V+ < VCM < 80V ?
  
2. In my circuit,
   V+   : 14V
   VIN+ : 50.000V
   VIN- : 49.980V  ( VSENCE = 20mV )

The following is schematics.
/cfs-file/__key/communityserver-discussions-components-files/14/INA193.pptx

How can I understund about output voltage accuracy?
Which is this circuit condition Case 3 or Case 2 of Device Functional Modes?

May I have your advice?
Thank you.

  • user6185632

    Part Number: INA193

    I changed the current 20mV to 10mV. And add more.

    I'm using INA193.

    The following is schematics.

    I hope to know about accuracy of output voltage.

    1. In the spec.sheet, There are many word "VS".
       VS is meaning V+ in my understunding.
       But there are word V+ and also Vsupply.
       

       
       In this sentence Case 3, Is it meaning VSENCE<20mV , V+ < VCM < 80V ?
       Can I use this ?


    2. In my circuit,
       V+   : 14V
       VIN+ : 50.000V
       VIN- : 49.990V  ( VSENCE = 10mV )

    How can I understund about output voltage accuracy?
    Which is this circuit condition , Case 3 or Case 2 of Device Functional Modes?

    May I have your advice?
    Thank you.

  • In reply to user6185632:

    Hello user6185632

    1. Yes. Vs is referring to the voltage at the V+ pin (pin 5 for INA193) of the device. We apologize for the confusion. Vs and V+ refer to the same thing.
    2. For your circuit, the following is true:
      1. Vs<VCM<80V
      2. Vsense = 10mV < 20mV
      3. This is case 3

    Unfortunately this is not a robust design. At 10mV, the output of INA193 should ideally be 20*10mV = 200mV; however, for Case 3 the INA193 output typically floors out at 300mV, meaning that VOUT cannot go lower than 300mV. This is also shown in the datasheet specifications table (section 7.5).

     

    Output voltage accuracy affected by input voltage offsets, device gain error, temperature drift, and linear operating region of the device. You will not want your Vsense to go any lower than 20mV or else device will be outside the device’s tested operating conditions. Consider increasing shunt resistance to increase Vsense. If Vsense is 20mV, this is how to calculate the worst-case (maximum) error.

    Vos_i = -2mV

    Vos_CMRR = (12V-50V)*10^(-80dB/20) =

    Vos_PSRR = (12V -14V)*100uV/V =

    Vos_total = -6mV

    Gain error max = 1%

    Calculate the total root-sum-square (RSS) error assuming the offset are correlated:

    Max Error at 20mV = SQRT( (6mV/20mV)^2 + 0.01^2 + Rshunt_tolerance^2)

    Assuming shunt tolerance is 0% in this equation, which it will never be, the Max Error at 20mV Vsense is 3.16%. Check out our training videos which explain many aspects of our devices (including error):

    https://training.ti.com/getting-started-current-sense-amplifiers

    Hope this helps,

    Peter

  • In reply to Peter Iliya:

    Hello Peter.

    Thanks for your explain. I understand.

    I hope to know one more.

    May I have a Electricl caracteristics curve for INA193 like as 8.4.2.3 Figure 26 ?

  • In reply to user6185632:

    Hey again user6185632,

    We do not have this data curve for the INA193, but as you have shown, you can determine the approximate behavior with INA193 and Vsense < 20mV given that only the gain changes from INA193 to INA195. What you have drawn seems appropriate. I have also included another way to visualize this curve for the INA193 by adding a second vertical VOUT scale (in blue) that the blue curve is plotted to.

    Overall, the main point here is that the gain begins to deviate as Vsense drops below 20mV and in order to achieve the specified performance Vsense needs to be greater than 20mV.

    I would recommend looking at a similar product (INA293-Q1) that has much better performance even when Vsense < 10mV.

    Sincerely,

    Peter Iliya

  • In reply to Peter Iliya:

    Hello Peter.

    I understood. 

    I will study about INA293-Q1.

    Thank you so much.