ZHCSN76B January 2021 – April 2022 DRV8316
PRODUCTION DATA
The SOx pins are typically sampled by an analog-to-digital converter in the MCU to calculate the phase current. Phase current calculations are used for closed-loop feedback such as Field-oriented control.
An example calculation for phase current is shown in Equation 21, Equation 22, and Equation 23 for a system using VREF = 3.0V, GAIN = 0.15 V/A, and a SOx voltage of 1.2V.
Sometimes high frequency noise can appear at the SOx signals based on voltage ripple at VREF, added inductance at the SOx traces, or routing of SOx 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, 22-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 24.
There is a small dynamic offset and gain error that appears at the SOB output when sinking larger currents into OUTB in applications such as 3-shunt Field-oriented control. Please check the DRV8316 errata for equations to manually implement in software to compensate for dynamic gain and offset errors at larger currents.