DRV2605L-Q1 Datasheet, PDF (10/67 Pages) Texas Instruments – Automotive Haptic Driver for LRA and ERM

DRV2605L-Q1
SLOS874A – OCTOBER 2015 – REVISED OCTOBER 2015
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7.3 Feature Description
7.3.1 Support for ERM and LRA Actuators
The DRV2605L-Q1 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 DRV2605L-Q1 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 the 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 I²C (see the LRA
Resonance Period (Address: 0x22) section). Because frequency reporting occurs in real time, it must be polled
while the DRV2605L-Q1 device synchronizes with the LRA. The data should not be polled when the actuator is
idle or braking.
7.3.2.3 Automatic Switch to Open-Loop for LRA
In the event that an LRA produces a non-valid back-EMF signal, the DRV2605L-Q1 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, the mode enjoys all of the benefits that the smart-loop
architecture has to offer.
¦_{(LRA_NO-BEMF)} |
1
u W_{(DRIVE_TIME[4:0])} ± W_{(ZC _ DET _ TIME[1:0])}
(1)
The DRV2605L-Q1 device offers an automatic transition to open-loop mode without the re-synchronization
option. The 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. The open-loop 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)
7.3.2.4 Automatic Overdrive and Braking
A key feature of the DRV2605L-Q1 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.
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