MCT8316AEVM: Tiny BLDC Motor Current (PWM=40KHz)

Hi Tom, 

Our team will follow up shortly and aim to provide a response before the end of the week. 

Best Regards, 
Andrew 

Hi Tom,

Thanks for posting your question in e2e forum. Channel 1 and 2 voltages are across which two pins of the device? Can you mention which phase current are you measuring on channel 4? Are you able to spin the motor or do you see any faults getting triggered? 

Regards,

Vishnu

Thanks for the reply, Vishnu. Channel 1 and 2 are voltage of OUTA and OUTB to PGND and Channel 4 is OUTA winding current (current probe direction reversed). No problem to spin the motor and no fault triggered.

Tom,

Can you zoom out the scope plot by increasing the time scale and share the plot again? Also, can you check if both the voltage probes are on same scaling (1x or 10x)?

Regards,

Vishnu

I will reconnect and run again. I'm certain that both probes have the same scaling. Because when OUTA low side is supposedly turned on, it has the same voltage waveform as OUTB shown above.

Vishnu, I think I know the reason for Ch2 voltage bump now. OUTB is in Hi-Z state therefore OUTB voltage is half of the voltage of OUTA to OUTC (GND in this case). My remaining question is what I can do to smooth the winding current. The tuning guide says to increase PWM frequency for low inductance motor. I can increase the PWM frequency to 60KHz but the current is still saw tooth like. Anything higher than that will give me Loss of Sync fault. Motor will not turn. Appreciate your guidance on the tuning procedure. Thanks! 

Tom,

Increasing the PWM switching frequency is the only option to smoothen the phase current in MCT8316A. We have MCF8316A which uses FOC algorithm and the phase current will look sinusoidal. 

Regards,

Vishnu