Different reading on shunt depending on motor direction

[Joshcm]

We have based this board off of  EVAL-L99H02QF.

We are having a difference in current reading on CSI2. We have 2 shunts, and the one that goes to GND R38 in my picture has a different reading whether motor is going one direction or the other. We cannot seem to understand why and are hoping someone has a good reason for this that we are missing. I would appreciate any feedback.

 

Thanks,

Josh

[Nickname4847_O]

Hello Josh

 

It is not possible to understand from the information what is happening, but I would try to decrease the current in the motor to understand if the measurements become identical again by changing the direction of the motor itself. This is because considering 120A of current with 2 mohms of resistance and gain equal to 10 we have a voltage to measure of 2.4V. This signal will be centered around Vdd/2 (3.3/2=1.65) and it could be that the system is working at the limit of its functionality. ?Maybe in one direction the current is slightly greater and we let the CSA saturate. So I would suggest you reduce the current and check if the error decreases or remains constant

Regards

Dino