SLOS854D May 2014 – March 2018 DRV2605L
In the event that an LRA produces a non-valid back-EMF signal, the DRV2605L device automatically switches to open-loop operation and continues to deliver energy to the actuator in overdrive mode at a default and configurable frequency. Use Equation 1 to calculate the default frequency. If the LRA begins to produce a valid back-EMF signal, the auto-resonance engine automatically takes control and continues to track the resonant frequency in real time. When synchronized, the mode enjoys all of the benefits that the smart-loop architecture has to offer.
The DRV2605L device offers an automatic transition to open-loop mode without the re-synchronization option. The feature is enabled by setting the LRA_AUTO_OPEN_LOOP bit in register 0x1F. The transition to open-loop mode only occurs when the driver fails to synchronize with the LRA. The AUTO_OL_CNT[1:0] bit in register 0x1F can be adjusted to set the amount of non-synchronized cycles allowed before the transition to the open-loop mode. Use Equation 2 to calculate the open-loop frequency. The open-loop mode does not receive benefits from the smart-loop architecture, such as automatic overdrive and braking.