DRV2624 Datasheet, PDF (12/79 Pages) Texas Instruments – DRV2624 Ultra Low Power Closed-Loop LRA/ERM Haptic Driver with Internal Memory

DRV2624
SLOS893A – DECEMBER 2015 – REVISED DECEMBER 2015
Feature Description (continued)
Same simple input for
both motors
Feedback provides
optimum output drive
www.ti.com
Input and output
Accleration
Output with feedback
Figure 17. Waveform Simplification With Smart Loop
8.3.2.4.1 Startup Boost
To reduce the actuator start-time performance, the DRV2624 device has an overdrive boost feature that applies
higher loop gain to transient response of the actuator.
8.3.2.4.2 Brake Factor
To optimize the actuator brake-time performance, the DRV2624 device provides a means to increase the gain
ratio between braking and driving gain. Higher feedback-gain ratios reduce the brake time, however, these ratios
also reduce the stability of the closed-loop system. The FB_BRAKE_FACTOR parameter can be adjusted to set
the brake factor.
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 this 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 DRV2624 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 the output level does not exceed the programmable overdrive clamp voltage.
8.3.2.5.1 Automatic Compensation for Resistive Losses
The DRV2624 device automatically compensates for resistive losses in the driver. During the automatic level-
calibration routine, the resistance of the actuator is checked and the compensation factor is determined and
stored in the A_CAL_COMP parameter.
8.3.2.5.2 Automatic Back-EMF Normalization
The DRV2624 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 parameter.
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 parameter can change the duration of the
automatic level-calibration routine to optimize calibration performance. Alternatively, the duration of the
calibration routine can be adjusted by the trigger by selecting the option in the AUTO_CAL_TIME parameter.
12
Submit Documentation Feedback
Product Folder Links: DRV2624
Copyright © 2015, Texas Instruments Incorporated