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DRV2604 Demonstration Program
2.2.3
Mode 3 – LRA Clicks
Mode 3 shows the difference in open-loop and closed-loop LRA clicks. In closed-loop the driver
automatically tracks the resonant frequency, and overdrives and brakes the actuator. In open-loop, the
waveform must be predefined with a static drive frequency, and overdrive and braking times. The image
on the left shows a closed-loop waveform and the image on the right shows a waveform with auto-
resonance off and no overdrive or braking.
Figure 7. LRA Closed-Loop Click Waveform (Button 1)
2.2.4
Mode 2 – Alerts and Scroll Wheel
Mode 2 showcases the advantages of the Smart Loop Architecture which includes auto-resonance
tracking, automatic overdrive, and automatic braking.
The two images below show the difference in acceleration between LRA auto-resonance ON and LRA
auto-resonance OFF. Notice that the acceleration is higher when driven at the resonant frequency. The
auto-resonance ON waveform has 1.32 G of acceleration and the auto-resonance OFF waveform has
0.92 G of acceleration. The auto-resonance ON waveform has 43% more acceleration.
Figure 9. LRA Auto-Resonance ON
Waveform (Button 1)
The reason for higher acceleration can be seen in the acceleration versus frequency graph below. The
LRA has a very narrow operating frequency range due to the properties of a spring-mass system.
Furthermore, the resonance frequency drifts over various conditions such as temperature and drive
voltage. With the Smart Loop auto-resonance feature, the DRV2604 dynamically tracks the exact resonant
frequency to maximize the vibration force.
8
DRV2604 ERM, LRA Haptic Driver Evaluation Kit
Figure 8. LRA Open-Loop Click Waveform (Button 4)
Copyright © 2013, Texas Instruments Incorporated
Figure 10. LRA Auto-Resonance OFF
Waveform (Button 2)
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SLOU355 – March 2013
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