INA193: Accuracy

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

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

Hello Peter.

I understood. 

I will study about INA293-Q1.

Thank you so much.