SLOS854D May 2014 – March 2018 DRV2605L
In the event that open-loop operation is desired (such as for off-resonance driving) the DRV2605L device includes an open-loop LRA drive mode that is available through the PWM input or through the digital interface.
When using the PWM input in open-loop mode, the DRV2605L device employs a fixed divider that observes the PWM signal and commutates the output drive signal at the PWM frequency divided by 128. To accomplish LRA drive, the host should drive the PWM frequency at 128 times the desired operating frequency.
When activated, the digital open-loop mode is available for pre-stored waveforms as well as for RTP mode. The OL_LRA_PERIOD bit in register 0x20 programs the operating frequency, which is derived from the PWM output frequency, ƒO(PWM). Use Equation 1 to calculate the driving frequency. The open-loop mode does not receive the benefits of the smart-loop architecture.