DRV2603_14 Datasheet, PDF (7/19 Pages) Texas Instruments – Haptic Drive with Auto-Resonance Detection for Linear Resonance Actuators (LRA)

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DRV2603
SLOS754A – JUNE 2012 – REVISED JANUARY 2014
APPLICATION INFORMATION
OPERATION
The DRV2603 is a haptic and vibratory driver designed specifically to meet the needs of haptic and vibration
applications in the portable market. The DRV2603 has two modes of operation, ERM mode and LRA mode. ERM
mode is designed to drive Eccentric Rotating Mass motors, which are generally DC motors of the bar or coin
type. LRA mode is designed to drive Linear Resonance Actuators, also known as linear vibrators, which
require an alternating signal that commutates at or very near the natural mechanical resonance frequency of the
actuator. These actuators present a unique control challenge that is solved in the DRV2603 by auto resonance
tracking.
CONSTANT VIBRATION STRENGTH
The DRV2603 features power supply feedback, so no supply regulation is required, and a direct battery
connection may be used. If the supply voltage drifts over time (due to battery discharge, for example), the
vibration strength will remain the same so long as there is enough supply voltage to sustain the required output
voltage. The DRV2603 PWM input also uses a digital level-shifter, so as long as the input voltage meets the V_IH
and V_IL levels, the vibration strength will remain the same even if the digital levels were to vary. These benefits
apply to both ERM mode and LRA mode.
LINEAR RESONANCE ACTUATORS
Linear Resonant Actuators, or LRAs, only vibrate effectively at their resonant frequency. LRAs have a high-Q
frequency response due to which there is a rapid drop in vibration performance at offsets of 2 to 3 Hz from the
resonant frequency. Many factors also cause a shift or drift in the resonant frequency of the actuator such as
temperature, aging, the mass the product to which the LRA is mounted, and in the case of a portable product,
the manner in which it is held. Furthermore, as the actuator is driven to its maximum allowed voltage, many
LRAs will shift several Hz in frequency due to mechanical compression. All of these factors make a real-time
tracking auto-resonant algorithm critical when driving LRA to achieve consistent, optimized performance.
f_RESONANCE
Frequency - Hz
Figure 11. Typical LRA Response
AUTO RESONANCE ENGINE FOR LRA
No frequency calibration or actuator training is required to use the DRV2603. The DRV2603 auto resonance
engine tracks the resonant frequency of an LRA in real time. If the resonant frequency shifts in the middle of a
waveform for any reason, the engine will track it cycle to cycle. The auto resonance engine accomplishes this by
constantly monitoring the back-EMF of the actuator. The DRV2603 tracking range for LRA devices is 140 Hz to
140 Hz.
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