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[FAQ] DRV2624: Principals and Method of Auto-Calibration for DRV2624 & DRV2625

Part Number: DRV2624
Other Parts Discussed in Thread: DRV2625

What is the purpose of auto-calibration?

- The auto-calibration routine is available for the purpose to drive the attached actuator into steady state based on the input parameters for rated voltage and clamp voltage, so that resistive losses can be compensated and the back-EMF can be normalized for correct smart loop algorithm function.

Does auto-calibration occur automatically?

- No just like the playback modes, the auto calibration mode must be selected and triggered in order for it to start

What input parameters must be written to in order to initialize the auto-calibration routine properly?

- Several parameters across several register addresses must written to for proper calibration to occur. Details about these parameters and steps to write to them can be found starting on page.28 in the DRV2625/2624 datasheets.

Does auto-calibration ever result in an error or improper results?

- There is a possibility of auto-calibration erring during its routine, if this occurs the DIAG_RESULT is set. The possibility of this occurring has largely to do with the amount of time allotted for the calibration to take place, in some cases the default of 250 ms can be too little time to reach steady-state and so the AUTO_CAL_TIME parameter is available to lengthen the time to 1 s or beyond.

Does auto-calibration affect auto-resonance tracking?

- While during the auto-calibration the initial resonant frequency has time to be set, the auto-resonance tracking works independently in monitoring and adjusting the resonant frequency over time.

What registers change as a result of the auto-calibration and how do I know when it has finished?

- Four registers are set by the auto-calibration including:  BEMF_GAIN[1:0],  A_CAL_COMP[7:0], A_CAL_BEMF[7:0], and DIAG_RESULT. The first three hold values that control the resistive loss compensation and back-EMF normalization, while DIAG_RESULT is set if an error occurred during the routine. When calibration is complete the GO bit will be cleared.