INA220: about Current readout value out of range

Hello Joyce,

Thanks for reaching out on the forum. From your register settings, I see that your customer is using the PGA = /4 setting as well as the 12 bit adc averaging measurement setting. If they are want to measure up to 65.535A, their shunt must be .16V/65.535A=0.002441or smaller. Assuming they used a .002441 ohm shunt, the current_LSB calculated from Equation 1 of the datasheet would be 0.005289A assuming cal=3172. Since your customer uses PGA=/4 setting, Equation 2 would change to: Maximum Expected Current/2^14. This formula yields a current_LSB of .004 A, which is smaller than your calibration current and allows for cal value of 3172. However, if your customer’s shunt has a wide tolerance, or if they decided to use a larger shunt, for instance 0.003ohm shunt, then their calibration current lsb will be larger than their actual measured current LSB, which would then be a problem.
Aside from this issue, I think your problem might actually be your initial setup or programming. Can you verify that your configuration register and calibration register are set to the values you expect them to be? Also can you monitor your communication between your master and your slave INA220 with an oscilloscope? I suspect your registers are not programmed correctly because you say your current register is the max value and to get your register you multiply your shunt voltage register by a ratio consisting of the calibration value over 4096. If the ratio is greater than 1 or cal >4096 it is possible to get the max 0xFFFF value. However, if the ratio is <1 like yours, since cal=3172, then it is impossible to reach 65535, because the shunt voltage register max is also 65535.

Hello Joyce,

We have not heard from you in a while, any updates?