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  • DRV2624 Ultra Low Power Haptic Driver

  • Created: Jun 16, 2016

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Summary

Haptic technology has been beneficial in virtual reality systems by recreating the sense of touch. This mechanical stimulation can be used to assist in the creation of virtual objects in a computer simulation, to control such virtual objects, and to enhance the remote control of machines and devices. It may also incorporate tactile sensors that measure forces exerted by the user on the interface.

This reference design is a typical application of a haptic driver that relies on a proprietary closed-loop architecture to deliver sharp, strong, and consistent haptic effects while optimizing power consumption. It has an application processor which makes the decision on when to execute haptic effects. This device has external buttons which fire different haptic effects when pressed. It uses the DRV2624 ultra low power closed loop LRA/ERM haptic driver that features an automatic go-to standby state and a battery preservation function to help reduce power consumption without user intervention. The NRST pin allows for a full shutdown state for additional power savings. In addition, it supports bit ERM and LRA actuators. Eccentric rotating-mass motors (ERMs) are typically DC-controlled motors of the bar or coin type. ERMs can be driven in the clockwise direction or counterclockwise direction depending on the polarity of voltage across the two pins while Linear resonant actuators (LRAs) vibrate optimally at the resonant frequency. LRAs have a high-Q frequency response because of a rapid drop in vibration performance at the offsets of 3 to 5 Hz from the resonant frequency The DRV2624 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 tracking by constantly monitoring the back-EMF of the actuator. In the event that an LRA produces a non-valid back-EMF signal, the device automatically switches to open-loop operation and continues to deliver energy to the actuator in overdrive mode at a default and configurable 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. During playback, if any of the output pins (OUT+ or OUT–) is shorted to VDD, GND, or to each other, a current protection circuit automatically enables to shut-down the output stage, the OC_DETECT bit is asserted (and an interrupt is fired if enabled) and the DRV2624 device will go into standby state. The DRV2624 device only checks for shorts when running a process (either RTP, waveform sequencer, diagnostics or calibration). If the short occurs when the device is idle, the short is not detected until the device attempts to run a process.


Haptic drivers have various applications such as used in automotive, personal electronics and medical devices. For automotive, one of the main ways to address the driver distraction issue is to use haptics to provide tactile feedback in driver controls. The driver can get the impression that they are pressing an actual button which brings significant value to the automotive user experience. Moreover, haptics can be used in portable medical devices to replace audible alerts with silent, discreet tactile alerts. In personal electronics, these devices will give the user a "real feel" to typing, clicking, scrolling, and swiping, on the capacitive touch display on their smartphone, tablet, or other device.


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