Haptic piezo controller helps to “feel the touch” in touch-screen applications

A novel haptic solution that provides customers with an enhanced, true “touch” experience with touch screens has been introduced Maxim Integrated Products which the company claims is the industry's first fully integrated, programmable HPC (haptic piezo controller) for single-layer and multilayer piezo actuators.

Consumers are accustomed to “feeling” the button press on keyboards, keypads, and many modern devices. Touch screens and capacitive sensors provide an interactive user interface, but the user cannot feel the touch because there is no mechanical button. The MAX11835 adds the feeling of mechanical feedback to touch screens and capacitive buttons. The product can be used with any touch-screen or touch-button controller. However, as part of its new TacTouch concept, Maxim provides design-in support and reference designs guaranteeing an optimal touch experience and simplified design-in when combined with the company's touch-screen controllers.

Target applications are any consumer or industrial equipment that has touch-screen displays or traditionally has mechanical buttons. Typical examples include cell phones, MIDs (mobile Internet devices), MP3 players, portable media players, digital photo frames, multifunction printers, digital still/video cameras, and POS (point-of-sale) terminals.

The MAX11835 expands the company's haptic product portfolio to drive piezo and other actuators requiring high-voltage signals. Single-layer piezo actuators are fairly mature and low cost, but they require higher voltage drives of up to 250 V. Multilayer piezo actuators, however, only require up to 40 V and thus eliminate additional high-voltage safety requirements in (handheld) products. Multilayer piezo actuators also support audio output, but are more expensive than single-layer piezo actuators.

The MAX11835 drives both single-layer and multilayer piezo actuators over a wide 5 V to 250 V voltage range. The wide output voltage range not only lets designers choose between these two types of piezo actuators, but also guarantees a future-proof solution for alternative actuator technologies. By integrating a user-programmable haptic pattern generator, programmable boost converter, and high-voltage, high capacitive load driver, the MAX11835 generates a user-configurable, slew-rate-limited, boosted voltage output.

The MAX11835 has sufficient on-chip memory to simultaneously store multiple user-defined haptic waveforms, which are downloaded at power-up through the serial I2C interface. During operation, only a haptic trigger pulse is required from the system or application processor to play out the waveform.

Unlike other driver ICs, no high-speed waveform pattern needs to be sent during operation. This simplifies code design on the system or application processor, reduces software load, and improves haptic response time.

Obtaining low latency (from the instant of touch detection to haptic response) is crucial to effectively mimic the real-world feeling of a button press.

The MAX11835 output drivers are able to drive highly capacitive loads, allowing the connection of multiple piezo actuators to a single device. This reduces total system cost, since only one IC is required in many applications.

The MAX11835 is designed for use in low-power handheld equipment and includes several power-saving modes, including an automatic power-saving mode between haptic events. A 400 kHz I2C serial interface allows programming of various modes of operation, status checking, and the programming of haptic waveforms.

Availability and pricing

The MAX11835 is packaged in a 25-pin WLP to support the miniaturization of end products. An EV (evaluation) kit is available to speed designs. To enable full system emulation and provide a total reference design, this EV kit comes with a resistive touch panel with piezo actuators mounted for evaluating the device's haptic feedback. Pricing for the MAX11835 starts at $1.40 (1000-up, FOB USA). Samples are available for qualified customers.



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