DRV2605L Datasheet, PDF (11/69 Pages) Texas Instruments – DRV2605L 2 to 5.2 V Haptic Driver for LRA and ERM With Effect Library and Smart-Loop Architecture

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DRV2605L
SLOS854C – MAY 2014 – REVISED SEPTEMBER 2014
8.3 Feature Description
8.3.1 Support for ERM and LRA Actuators
The DRV2605L 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.
8.3.2 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.
8.3.2.1 Auto-Resonance Engine for LRA
The DRV2605L 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.
8.3.2.2 Real-Time Resonance-Frequency Reporting for LRA
The smart-loop architecture makes the resonant frequency of the LRA available through I²C (see the LRA
Resonance Period (Address: 0x22) section). Because frequency reporting occurs in real time, it must be polled
while the DRV2605L device synchronizes with the LRA. This data should not be polled when the actuator is idle
or braking.
8.3.2.3 Automatic Switch to Open-Loop for LRA
In the event that an LRA produces a non-valid back-EMF signal, the DRV2605L device automatically switches to
open-loop operation and continues to deliver energy to the actuator in overdrive mode at a default and
configurable frequency. Use Equation 1 to calculate the default frequency. If the LRA begins to produce a valid
back-EMF signal, the auto-resonance engine automatically takes control and continues to track the resonant
frequency in real time. When synchronized, this mode enjoys all of the benefits that the smart-loop architecture
has to offer.
  ^{¦(LRA_NO-BEMF) |  u}
1
W_{(DRIVE_TIME[4:0])} ± W_{(ZC _ DET _ TIME[1:0])}
(1)
The DRV2605L device offers an automatic transition to open-loop mode without the re-synchronization option.
This feature is enabled by setting the LRA_AUTO_OPEN_LOOP bit in register 0x1F. The transition to open-loop
mode only occurs when the driver fails to synchronize with the LRA. The AUTO_OL_CNT[1:0] bit in register 0x1F
can be adjusted to set the amount of non-synchronized cycles allowed before the transition to the open-loop
mode. Use Equation 2 to calculate the open-loop frequency. This mode does not receive benefits from the smart-
loop architecture, such as automatic overdrive and braking.
¦_{(LRA_OL)}
1
OL_LRA_PERIOD[6:0] × 98.49 × 10^±
(2)
8.3.2.4 Automatic Overdrive and Braking
A key feature of the DRV2605L 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.
Copyright © 2014, Texas Instruments Incorporated
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