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DRV2605: Autocalibration issues

Part Number: DRV2605

We are trying to use the DRV2605 built-in Auto-Calibration and diagnostic functionalities with an 8mm LRA, but it seems to fail very often. Autocalibration sometimes works, while LRA diagnostics almost always fails. It also depends on how the enclosure is held; certain positions make it fail every time. The LRA still vibrates however, even when Autocalibration and/or diagnostics fail.

The DRV2605 is powered by a 5.00V regulator.

The LRA internal construction includes a central coil, with a magnetic ring weight on a spring. Total weight is 1g. It operates at 235Hz, has rated voltage of 1.8VAC, and acceleration of 1.4G. (MPN G0832013D).

We found a set of parameters that seems to produce reliable and strong vibration. However, we are worried that the LRA loses frequency track and that is why Autocalibration and diagnostics often fail.

Is our issue with initial parameters, or should we look at the LRA adhesion inside our enclosure? Currently, the LRA is pressed by a layer of foam against an internal surface; we were however also considering having it glued firmly to the surface instead.

Also, in our experience, the DRV2605 worked much better when we were using an LRA with inverse construction: central magnet with moving coil on the weight. With that LRA, the autocalibration and diagnostic routines passed almost every time.

The best initial parameters we found for G0832013D:

LRA Control Reg1: 144

LRA Control Reg2: 245

LRA Rated Voltage: 78

LRA OD Clamp Voltage: 228

LRA Feedback Control: 177

BEMF Gain: 3

I tried parameter sweeps with all of these parameters to find optimal values; I have however not modified any of the "Advanced User" parameters. Would they help with this?