SLOS825E December 2012 – April 2018 DRV2605
The resonance frequency of each LRA actuator varies based on many factors and is generally dominated by mechanical properties. The auto-resonance engine-tracking system is optimized by providing information about the resonance frequency of the actuator. The DRIVE_TIME[4:0] bit is used as an initial guess for the half-period of the LRA. The drive time is automatically and quickly adjusted for optimum drive. For example, if the LRA has a resonance frequency of 200 Hz, then the drive time should be set to 2.5 ms.
For ERM actuators, the DRIVE_TIME[4:0] bit controls the rate for back-EMF sampling. Lower drive times imply higher back-EMF sampling frequencies which cause higher peak-to-average ratios in the output signal, and requires more supply headroom. Higher drive times imply lower back-EMF sampling frequencies which cause the feedback to react at a slower rate.