ZHCSQQ0A June 2022 – October 2022 DRV8329
PRODUCTION DATA
The SO pin is typically sampled by an analog-to-digital converter in the MCU to calculate the total motor phase current. A phase current calculation is used for closed-loop feedback such as overcurrent protection or sensorless trapezoidal or Field-oriented control commutation
An example calculation for phase current is shown below for a system using VSO = 1.4 V, VCSAREF = 3.3V, CSAGAIN = 20 V/V, and RSENSE = 1 mΩ.
Sometimes high frequency noise can appear at the SO signals based on voltage ripple at VREF, added inductance at the SO traces, or routing of SO traces near high frequency components. It is recommended to add a low-pass RC filter close to the MCU with cutoff frequency at least 10 times the PWM switching frequency for trapezoidal commutation and 100 times the PWM switching frequency for sinusoidal commutation to filter high frequency noise. A recommended RC filter is 330-ohms, 470-pF to add minimal parallel capacitance to the ADC and current mirroring circuitry. The cutoff frequency for the low-pass RC filter is in Equation 16.