SLVSE89C August 2017 – June 2020 DRV10987
The DRV10987 device offers four methods for indirectly controlling the speed of the motor by adjusting the output voltage amplitude. This can be accomplished by varying the supply voltage (VCC) or by controlling the speed command. The speed command can be controlled in one of three ways. The user can set the speed command by adjusting either the PWM input (PWM in) or the analog input (Analog) or by writing the speed command directly through the I2C serial port (I2C). The speed command is used to determine the PWM duty cycle output (PWM_DCO) (see Figure 9).
The PWM input (PWM in) can have a minimum duty cycle limit applied. DutyCycleLimit[1:0], accessible through the I2C interface, allows the user to configure the minimum duty cycle behavior. This behavior is illustrated in Figure 8.
The speed command may not always be equal to the PWM_DCO because the DRV10987 device has the AVS function (see Anti-Voltage Surge Function), the software current-limit function (see Software Current Limit), and the closed-loop accelerate function (see Closed-Loop Accelerate) to optimize the control performance. These functions can limit the PWM_DCO, which affects the output amplitude (see Figure 9).
The output voltage amplitude applied to the motor is developed through sine wave modulation so that the phase-to-phase voltage is sinusoidal.
When any phase is measured with respect to ground, the waveform is sinusoidally coupled with third-order harmonics. This encoding technique permits one phase to be held at ground while the other two phases are pulse-width modulated. Figure 10 and Figure 11 show the sinusoidal encoding technique used in the DRV10987 device.
|Sinusoidal Voltage From Phase to Phase||Sinusoidal Voltage With Third-Order Harmonics From Phase to GND|
The output amplitude is determined by the magnitude of VCC and the PWM duty cycle output (PWM_DCO). The PWM_DCO represents the peak duty cycle that is applied in one electrical cycle. The maximum amplitude is reached when PWM_DCO is at 100%. The peak output amplitude is VCC. When the PWM_DCO is at 50%, the peak amplitude is VCC / 2 (see Figure 12).
Motor speed is controlled indirectly by controlling the output amplitude, which is achieved by either controlling VCC, or controlling the PWM_DCO. The DRV10987 device provides different options for the user to control the PWM_DCO:
See the Closed Loopsection for more information.