INA240-Q1: Basic question

Hello Takumi,

Q1) The Reference Voltage Rejection Ratio (RVRR) is similar the Common Mode Rejection Ratio in that changing the reference voltage (Vref) induces a change in the input offset voltage, so you are right. The error is calculated by first determining what Vref is (where Vref = (Vref1 + Vref2)/2 ) and then insert into the equation below from Table 3 of the datasheet. In the example below Vref1 = Vref2 = 0V and the gain variant was A4 (RVRR = 2uV/V).

Q2) Vref1 an Vref2 pins are ideally meant to be driven with low-impedance sources. Driving Vref1 and Vref2 pin with a resistor divider network seen in Figure 31 is not ideal because the resistors (R1 and R2) will be loading down the internal reference resistor network causing common mode and differential errors on the output. These errors are from "internal impedance shifts" because the internal impedances are imbalanced by the external resistors R1 and R2. If one uses the confiugration of Figure 31, then it is best to output the signal differentially because the common mode errors from R1 and R2 will be removed. So if one decides to use Figure 31, but output the signal as a single ended signal with respect to GND, then the common mode error will appear cause significant error.

These common mode and differential errors due to R1 and R2 can be calculated with equations seen in this post:

Sincerely,

Peter Iliya

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