Haptics-Driver IC Enhances LRA, VCM Performance and User Experience

Haptics is more than a basic touchscreen with fixed virtual buttons. It provides visual and tactile feedback, and dynamically adapts to the user’s situation, flow, and requirements. Passive haptics has basic buttons and doesn’t inherently involve a display screen, while active haptics adds scrolling, feel, and feedback. The increasing incorporation of haptics-enabled designs to create a more advanced, multidimensional user experience (often called out simply as “the UE”), in addition to supplementing basic operation, means that the haptics actuators need sophisticated drive functionality.

For example, automobiles, PCs, wearables, and game controllers are moving beyond traditional button interfaces to incorporate non-mechanical haptic feedback. Driving this shift, improved haptics-related components and software are enabling design of sleeker, more-robust end products with fewer mechanical controls. Still, there’s an increased number of interactive options for the user, more and better user feedback, and improved dynamic performance for even-more responsive and immersive user experiences.

To meet the evolving needs of designers needing (or wishing) to incorporate haptics functionality into their products, Cirrus Logic introduced its CS40L25 family of ICs, which integrate a high-performance haptic driver, digital signal processor, and boost converter. These ICs (Fig. 1), which differ primarily in their packaging options (30-ball WLCSP, 32-pin QFN), AEC-Q100 rating, and some package-pin functions, can drive both high-performance linear-resonant actuators (LRAs) with impedances as low as 6 Ω as well as voice-coil motors (VCMs), and do so with ultra-low latency to provide real-time control of the haptic motor.

1. The CS40L25 family of haptics driver ICs developed by Cirrus Logic provides a sophisticated, high-power driver between the system processor and the end-effector linear-resonant actuator (LRA) or voice-coil motor (VCM).

Closed-loop algorithms maximize LRA effectiveness and support strong and consistent haptics with a crisper, less “buzzy” effect while also offering a more immediate sensation or response. In addition, these ICs support unique, user-supplied, pre-stored haptic waveforms. Other features include:

On-going resonance-frequency calibration at the system level for the LRA to maximize performance and efficiency, which further enables strong and consistent haptics. The algorithms also enhance protection of the LRA from over-excursion and provide for overall long-term reliability of the LRA.
An algorithm that dynamically handles changes in actuator characteristics to eliminate the need to fine-tune for long hours, including closed-loop algorithms that maximize LRA effectiveness (Fig. 2).
Always-on listening for a haptic-event trigger to reduce time from trigger event to achieving desired acceleration on the LRA, with a wakeup from hibernate mode in 5 ms.
Extremely low hiberation current of under 20 μA while listening for a user “trigger.”
Output voltage- and current-monitoring software.
Triggered haptic actuator-impedance and resonance-frequency reporting.
Pre-stored haptic waveforms that can be triggered by I²C/GPI for gaming applications and user-interface events.
Flexible haptic-waveform generation that can be triggered by GPI for home-button or side-button switch replacement.

2. Within the very similar CS40L25 ICs are the functional blocks and firmware needed for advanced closed-loop control of the actuator, resulting in superior performance with respect to responsiveness, control, tuning, adaptiveness, and longevity.

Driving haptics actuators is also about power—specifically, using as little as possible while delivering the relatively large amount required by the actuator. These ICs incorporate a Class H digital-boost converter with 85% overall efficiency boost and programmable boost voltages up to 11 V. The high-bandwidth digital-control loop has a 2-MHz switching frequency along with a pulse-skipping mode for improved efficiency during low-power quiescent operation.

System protection—always a good idea when driving real-world external loads—includes thermal self-protection for the IC against overtemperature, battery-rail reactive-brownout system protection, and speaker-current sensing via an integrated current-monitoring resistor. More information on the Cirrus Logic CS40L25 portfolio and its haptic technology is available at the company’s product and family overview page.