Greetings,
I’m working on a project of Reconstructing Stepper Motor Torques by sampling its Phase Currents using ACS721 (5A version). (for your interest) The equation that relates Phase Currents and Torque is:
The Stepper is drived by a Stepper Driver (TB6600) which use PWM and the ACS721 senses the Phase Currents using Inline Current Sensing configuration. Stepper is running on 1/16 MicroStepping mode with the PWM Freq at peak is 9kHz. My only concern is at what frequency should the ACS721 samples? I did found some using 2xPWM freq, some using 10xPWM freq (this exceeds ACS721 bandwidth).
Thank you for your attention ! 
Hello.
Can you specify which of our products you are using? In general my advice for something like this is to start by reading the sensor at the fastest rate possible. Then looking at the results of that will probably give you some ideas for how you should proceed.
- Patrick
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To obtain a reasonable representation of the waveform for later analysis, most people would use a sample frequency of at least 10X PWM frequency and preferably higher. If that exceeds the current sensor bandwidth, choose a different sensor.