SLVSEE8B November 2019 – May 2021 DRV8899-Q1
The current through the motor windings is regulated by a PWM current-regulation circuit. When an H-bridge is enabled, current rises through the winding at a rate dependent on the DC voltage, inductance of the winding, and the magnitude of the back EMF present. When the current hits the current regulation threshold, the bridge enters a decay mode for a period of time determined by the TOFF register setting and the selected decay mode to decrease the current. After the off-time expires, the bridge is re-enabled, starting another PWM cycle.
The PWM regulation current is set by a comparator which monitors the voltage across the current sense MOSFETs in parallel with the low-side power MOSFETs. The current sense MOSFETs are biased with a reference current that is the output of a current-mode sine-weighted DAC whose full-scale reference current is set by the voltage at the VREF pin. In addition, the TRQ_DAC register can further scale the reference current.
Use Equation 1 to calculate the full-scale regulation current.
The TRQ_DAC is adjusted via the SPI register. Table 7-6 lists the current scalar value for different inputs.
|TRQ_DAC||CURRENT SCALAR (TRQ)|