Oversized Filter Capacitors on EVSPIN32G4-DUAL Can Cause Encoders To Not Work At Higher Speeds

[Brohanlo]

Hello,

I am using a EVSPIN32G4-DUAL board to drive a 48V BLDC motor and using an encoder for speed feedback.

After a week of troubleshooting I was able to determine why my motor project could not achieve speeds above 700 RPM. The board has RC lowpass filters on the encoder / Hall sensor lines. The capacitor is oversized (1nF) and gives a lowpass cutoff frequency of about 16kHz. For comparison, my encoder with 2500 pulses per revolution spinning at 700 RPM yields about 29kHz. So at and above 700 RPM the encoder signal was becoming attenuated by the filter and could not be detected by the microcontroller.

I was able to solve this by removing the 1nF capacitors and replacing them with 12pF.

For example, the STEVAL-CTM015A1 uses 1.8K resistors and 10pF capacitors for the same purpose. So, it would be helpful if someone at ST could update the documentation or software to provide a warning when using this board and encoders at high speeds.

[GMA · Accepted solution]

Hello @Brohanlo,

Thank you for your problem report.
A warning message will be introduced on the Motor Control workbench user interface to replace RC resistor from 10kΩ to 330Ω to increase cutoff frequency.

This warning message will be present in our next release and will cover both EVSPIN32G4 and EVSPIN32G4-DUAL boards.