SLVSI02 May 2025 DRV8376-Q1
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 of SOx voltage is shown below, for a system using VVREF = 3.3V, GAIN = 1V/A, and peak motor current (IOUTx) of ±1.25A.
Sometimes high-frequency noise appears at the SOx signals due to voltage ripple at VREF, added inductance in the SOx traces, or the proximity of SOx traces to high-frequency components. Adding a low-pass RC filter near the MCU, with a cutoff frequency at least 10 times the PWM switching frequency for trapezoidal commutation and 100 times the PWM switching frequency for sinusoidal commutation, effectively eliminates high-frequency noise. Selecting the capacitor depends on various parameters, such as bandwidth requirements, ADC sampling capacitor, and ADC acquisition time. The current sensing output stage manages only currents in the order of a few hundred micro-amperes. Using a capacitor with a maximum value of 100pF maintains optimum performance. Choose a resistor based on the bandwidth requirements. The cutoff frequency for the low-pass RC filter is in Equation 13.