DRV2605L Datasheet, PDF (12/69 Pages) Texas Instruments – DRV2605L 2 to 5.2 V Haptic Driver for LRA and ERM With Effect Library and Smart-Loop Architecture

DRV2605L
SLOS854C – MAY 2014 – REVISED SEPTEMBER 2014
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Feature Description (continued)
An open-loop haptic system typically drives an overdrive voltage at startup that is higher than the steady-state
rated voltage of the actuator to decrease the startup latency of the actuator. Likewise, a braking algorithm must
be employed for effective braking. When using an open-loop driver, these behaviors must be contained in the
input waveform data. Figure 12 shows how two different ERMs with different startup behaviors (Motor A and
Motor B) can both be driven optimally by the smart-loop architecture with a simple input for both motors. The
smart-loop architecture works equally well for LRAs with a combination of feedback control and an auto-
resonance engine.
Ideal Open-Loop Waveform for Motor A
Ideal Open-Loop Waveform for Motor B
Same simple input for
both motors
Feedback provides
optimum output drive
Input and output
Accleration
Output with feedback
Figure 12. Waveform Simplification With Smart Loop
8.3.2.4.1 Startup Boost
To reduce the actuator start-time performance, the DRV2605L device has an overdrive boost feature that applies
higher loop gain to transient response of the actuator. The STARTUP_BOOST bit enables this feature.
8.3.2.4.2 Brake Factor
To reduce the actuator brake-time performance, the DRV2605L 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[2:0] bits can be adjusted to set the
brake factor.
8.3.2.4.3 Brake Stabilizer
To improve brake stability at high brake-factor gain ratios, the DRV2605L device has a brake-stabilizer
mechanism that automatically reduces the loop gain when the braking is near completion. The
BRAKE_STABILIZER bit enables this feature.
12
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