DRV2604L Datasheet, PDF (14/73 Pages) Texas Instruments – DRV2604L 2- to 5.2-V Haptic Driver for LRA and ERM with Internal Memory and Smart-Loop Architecture

DRV2604L
SLOS866D – MAY 2014 – REVISED JUNE 2015
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Feature Description (continued)
8.3.2.5 Automatic Level Calibration
The smart-loop architecture uses actuator feedback by monitoring the back-EMF behavior of the actuator. The
level of back-EMF voltage can vary across actuator manufacturers because of the specific actuator construction.
Auto calibration compensates for the variation and also performs scaling for the desired actuator according to the
specified rated voltage and overdrive clamp-register settings. When auto calibration is performed, a 100% signal
level at any of the DRV2604L input interfaces supplies the rated voltage to the actuator at steady-state. The
feedback allows the output level to increase above the rated voltage level for automatic overdrive and braking,
but without allowing the output level to exceed the programmable overdrive clamp voltage.
In the event where the automatic level-calibration routine fails, the DIAG_RESULT bit in register 0x00 is asserted
to flag the problem. Calibration failures are typically fixed by adjusting the registers associated with the automatic
level-calibration routine or, for LRA actuators, the registers associated with the automatic-resonance detection
engine. See the Device and Documentation Support section for automatic-level calibration programming.
8.3.2.5.1 Automatic Compensation for Resistive Losses
The DRV2604L device automatically compensates for resistive losses in the driver. During the automatic level-
calibration routine, the impedance of the actuator is checked and the compensation factor is determined and
stored in the A_CAL_COMP[7:0] bit.
8.3.2.5.2 Automatic Back-EMF Normalization
The DRV2604L device automatically compensates for differences in back-EMF magnitude between actuators.
The compensation factor is determined during the automatic level-calibration routine and the factor is stored in
the A_CAL_BEMF[7:0] bit.
8.3.2.5.3 Calibration Time Adjustment
The duration of the automatic level-calibration routine has an impact on accuracy. The impact is highly
dependent on the start-time characteristic of the actuator. The auto-calibration routine expects the actuator to
have reached a steady acceleration before the calibration factors are calculated. Because the start-time
characteristic can be different for each actuator, the AUTO_CAL_TIME[1:0] bit can change the duration of the
automatic level-calibration routine to optimize calibration performance.
8.3.2.5.4 Loop-Gain Control
The DRV2604L device allows the user to control how fast the driver attempts to match the back-EMF (and thus
motor velocity) and the input signal level. Higher loop-gain (or faster settling) options result in less-stable
operation than lower loop gain (or slower settling). The LOOP_GAIN[1:0] bit controls the loop gain.
8.3.2.5.5 Back-EMF Gain Control
The BEMF_GAIN[1:0] bit sets the analog gain for the back-EMF amplifier. The auto-calibration routine
automatically populates the bit with the most appropriate value for the actuator.
Modifying the SAMPLE_TIME[1:0] bit also adjusts the back-EMF gain. The higher the sample time, the higher
the gain.
By default, the back-EMF is sampled once during a period. In the event that a twice per-period sampling is
desired, assert the LRA_DRIVE_MODE bit.
8.3.2.6 Actuator Diagnostics
The DRV2604L device is capable of determining whether the actuator is not present (open) or shorted. If a fault
is detected during the diagnostic process, the DIAG_RESULT bit is asserted.
8.3.2.7 Automatic Re-Synchronization
For the LRA, the DRV2604L device features an automatic re-synchronization mode which automatically pushes
the actuator in the correct direction when a waveform begins playing while the actuator is moving. If the actuator
is at rest when the waveform begins, the DRV2604L device drives in the default direction.
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