Data Sheet

Input and output

Accleration

Ideal Open-Loop Waveform for Motor A

Output with feedback

Ideal Open-Loop Waveform for Motor B

Same simple input for

both motors

Feedback provides

optimum output drive

DRV2605L

SLOS854C –MAY 2014–REVISED SEPTEMBER 2014

www.ti.com

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.

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.

Product Folder Links: DRV2605L