DRV2603_14 Datasheet, PDF (8/19 Pages) Texas Instruments – Haptic Drive with Auto-Resonance Detection for Linear Resonance Actuators (LRA)

DRV2603
SLOS754A – JUNE 2012 – REVISED JANUARY 2014
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LRA MODE
When in LRA mode, the DRV2603 employs a simple control scheme that is designed to be compatible with ERM
mode signaling. A 100% input duty cycle gives full vibration strength, and a 0% to 50% input duty cycle gives no
vibration strength. The auto resonance detection algorithm takes care of the physical layer signaling and
commutation required by linear resonance actuators. The DRV2603 implements closed-loop operation
comprising a simple feedback loop. If the back-EMF feedback tells the device that the vibration is too low relative
to the input duty cycle, the DRV2603 will increase the vibration strength. If the back-EMF feedback tells the
device that the vibration is too high relative to the input duty cycle, the DRV2603 automatically enforces a
braking algorithm. It follows that a 0% to 50% input duty cycle will always enforce braking until the LRA is no
longer moving. This form of signaling is used to preserve the same input format for both ERM and LRA drive;
therefore, no software changes are required when switching between ERMs and LRAs with the DRV2603.
Steady-State
Output Drive
2.2 Vrms
1.1 Vrms
Full Braking
Input
0%
50%
75%
100%
PWM Input Duty Cycle
Figure 12. LRA Mode
The exact full-scale output voltage depends on the physical construction of the LRA itself. Some LRA devices
give a small amount of back-EMF during full scale vibration, and other LRA devices give a much larger amount.
A nominal full-scale output value is 2.2 V_RMS, but it can typically vary as much as +/- 10% depending on the
actuator's physical design. The output voltage can be approximated by the following equation between 50% and
100% input duty cycle.
spacer
V V OUT (RMS) = OUT (FULL-SCALE)
éInput Duty Cycle %
êë
50
-
ù
1_úû
(1)
Since the DRV2603 includes constant output drive over supply voltage, the output PWM duty cycle will be
adjusted so that the relationship in the above equation will hold true regardless of the supply voltage.
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