Datasheet

DRV2605

SLOS825C –DECEMBER 2012 –REVISED SEPTEMBER 2014

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7.3 Feature Description

7.3.1 Support for ERM and LRA Actuators

The DRV2605 device supports both ERM and LRA actuators. The ERM_LRA bit in register 0x1A must be

configured to select the type of actuator that the device uses.

7.3.2 Smart-Loop Architecture

The smart-loop architecture is an advanced closed-loop system that optimizes the performance of the actuator

and allows for failure detection. The architecture consists of automatic resonance tracking and reporting (for an

LRA), automatic level calibration, accelerated startup and braking, diagnostics routines, and other proprietary

algorithms.

7.3.2.1 Auto-Resonance Engine for LRA

The DRV2605 auto-resonance engine tracks the resonant frequency of an LRA in real time, effectively locking

onto the resonance frequency after half of a cycle. If the resonant frequency shifts in the middle of a waveform

for any reason, the engine tracks the frequency from cycle to cycle. The auto-resonance engine accomplishes

this tracking by constantly monitoring the back-EMF of the actuator. The auto-resonance engine is not affected

by the auto calibration process, which is only used for level calibration. No calibration is required for the auto

resonance engine. See the Auto-Resonance Engine Programming for the LRA section for auto-resonance engine

programming information.

7.3.2.2 Real-Time Resonance-Frequency Reporting for LRA

The smart-loop architecture makes the resonant frequency of the LRA available through I

C (see the LRA

Resonance Period (Address: 0x22) section). Because frequency reporting occurs in real time, it must be polled

while the DRV2605 device synchronizes with the LRA. This data should not be polled when the actuator is idle or

braking.

7.3.2.3 Automatic Overdrive and Braking

A key feature of the DRV2605 is the smart-loop architecture which employs actuator feedback control for both

ERMs and LRAs. The feedback control desensitizes the input waveform from the motor-response behavior by

providing automatic overdrive and automatic braking.

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 11 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.

Product Folder Links: DRV2605