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# MCT8316Z: Calculating max motor current

Part Number: MCT8316Z

My customer question:

I was referring the attached sheet for calculating the maximum current supported by the MCT8316Z device. The sheet is downloaded from https://www.ti.com/. I have few queries related to same.

Can you please clarify what is Motor Electrical Frequency and PWM Frequency?

BLDC_Int_Fet_Thermal_Calculator_V3.xlsx

• Hi Frank,

The MCT8316Z supports 8-A peak current and about 5.65-A RMS current. The relationship between RMS and peak current for trapezoidal commutation is:

For the thermal calculator, electrical frequency at the RMS current of the motor application is used in the tool to calculate junction temperature. The electrical frequency can be measured or calculated as below:

1) measured on an oscilloscope using a current probe

2) calculated based on the mechanical speed of the motor using RPM = (60 * electrical frequency) / (# pole pairs).

You can determine the RPM of the motor under known load conditions using the motor's load curve or torque-speed curve.

PWM frequency is the frequency the motor voltage switches at, which is determined by the PWM frequency of the PWM input. Typical PWM frequency for a BLDC motor is 20kHz.

Thanks,
Aaron