Tactile feedback effects (commonly referred to as haptics) are an increasingly important component of both consumer and industrial applications, especially as touch screens become more prevalent. Users love touch screens, but they also love the feedback and satisfaction they get from pushing a physical button, which makes haptic feedback all the more important. TI just introduced the DRV8662, a piezo haptic driver that enables what we call "high-definition haptics."
Piezo actuators come in a few varieties. Primarily, they are either disks or benders (also called beams), as shown in Figure 1, and within those segments you have high-voltage (or single layer) and low-voltage (multi-layer) piezo elements.
Figure 1: Piezo actuators are typically either disks or benders.
Benders and disks have their differences. As a voltage is applied to a bender, it transforms from its normal flat form into a bent U-shape. Applied in a horizontal direction, this can enable a "floating screen" - a screen that is free to move in one dimension within its casing - to create localized haptics.
Localized haptics refers to the circumstance wherein you feel the haptic vibration within the screen itself, as opposed to "whole body haptics," when a vibration is felt throughout the entire device (such as when you feel a text message alert in your pocket). To mount the device, typically the ends of the bender are fixed to the case and the middle of the bender is fixed to the screen. As the bender goes from flat to bent, the screen will move in that one dimension of freedom. Take a look at Figure 2.
Figure 2: The typical mounting scheme for piezo haptic actuators.
Disks, on the other hand, must be used in a set of four and set at each corner of the touch screen. Unlike the bender moving from flat to a U shape, the disk will transform itself from flat and button-like to a smaller radius and taller height, causing a translation in the z-axis. This process creates a vibration effect, as well as a small audible pop noise.
The DRV8662 is capable of driving both of these types of piezo actuators, from high-voltage actuators at 200-Volts peak-to-peak (Vpp) with typical loads of around 100-nanofarad (nF), all the way down to low-voltage piezos at 50-Vpp with the higher load of 680nF. The driver features an ultra-fast start-up time of 1.5-milliseconds, 30 to 60 times faster than inertial-based haptic drivers.
The DRV8662 is the industry's most highly integrated piezo haptic driver and does not require an external transformer for flyback setup. The device also features an integrated 100-V boost converter and power FET. This not only reduces the total system solution size by 50%, but it also provides for a total solution cost that is 40% lower.