Achieve Precision Control of Vibration for Wearables
January 4, 2018
|By: Frank Dowling
Business Director, Industrial & Healthcare Business Unit, Maxim Integrated
Many applications now incorporate haptics technology, delivering an immersive and more engaging experience through the sense of touch. We’re even seeing the magic of haptics in wearables. Smartwatches can vibrate to notify you that you've made a wrong turn on your hike. They can do the same while you’re on a run, informing you that you’re either behind or on your targeted pace. And who doesn't appreciate the convenience of having one particular vibration to alert you that your boss is calling and another for calls from your significant other?
However, integrating haptics into wearables isn’t easy, given that space is already constrained and power consumption is a big challenge. One way to overcome the obstacles is to incorporate a power management IC (PMIC) into your design.
PMICs for haptic applications—particularly products like wearables, portable devices ,and even some internet of things (IoT) gadgets—need to meet stringent requirements for small form factor and high efficiency. Often, these types of products spend a lot of their time in standby mode, waking periodically to perform some task. That’s why it’s essential for standby current drawn from the battery to be as low as possible, in order to help extend the device’s battery life. Based on these criteria, some system designers conclude that the best approach is to minimize their system’s quiescent current by simplifying their power architecture and only incurring the quiescent current of a single converter to supply the whole system. For example, they might designate a single 3V supply for powering the whole system, using load switches to disconnect portions of the circuit to preserve battery life when these portions are inactive. However, the problem with this approach is that, while the standby current is minimized, the optimal average current has not been reached because of the higher power consumption in active mode. As a result, the average power over the battery charge cycle is not optimized.
Enabling High-Fidelity Haptic Effects
Many of today’s wearables utilize eccentric rotating mass (ERM) actuators to create the vibration. Like a regular DC motor, an ERM motor uses the magnetic field of a direct electrical current to move an object in a circle. By contrast, with linear resonant actuators (LRA), designers can create more sophisticated vibration signals that convey contextual information to device wearers. LRA uses a voice coil which, based on an AC input, produces a corresponding vibration with a frequency and amplitude that correspond to the provided electrical signal. They’re more complex, but LRAs do generally consume less power to produce a vibration than do ERMs. With PMICs, some similar criteria apply; in other words, PMICs that minimize the battery power required to create particular vibrations are ideal.
To sufficiently address the power-related design challenges of wearables with haptics functionality, PMICs should have:
- Regulators with ultra-low quiescent current, which reduces standby power for always-on resources, extends battery life, and reduces battery size
- Efficient regulators that reduce active power while also extending battery life and reducing battery size
- Integration to support a sophisticated power architecture in space-constrained designs
- System management, with elements including switching noise mitigation, unified I2C control, integration button/reset control, and a fuel gauge
- And a power-efficient haptics driver
Maxim has announced a new PMIC that is the first on the market to provide a haptic driver. The MAX20303 PMIC for ultra-low-power wearables features an ERM/LRA haptic driver with automatic resonance tracking. The PMIC's power management capabilities extend battery charge, and the part is available in a 3.71mm x 4.21mm wafer-level package (WLP). The MAX20303 also features:
- Micro quiescent current boost and buck regulators
- Integrated linear Li-ion battery charger, micro quiescent current low-dropout (LDO) regulators, and current sinks
- Power on/reset controller, I2C configurability, and optional fuel gauge
Application block diagram of the MAX20303, a highly integrated and programmable power management solution for ultra-low-power wearables.
Consider, as an example application, a GPS sports watch. In this watch, the MAX20303 can provide all of the power rails for the processor, the sensors, the GPS, and the Bluetooth Low Energy interface. It can also charge the battery, monitor the battery state-of-charge, and provide haptic feedback to the user.
Consumer, Medical, and Automotive Applications Driving Growth in Haptic Technology
According to analysis from researchers at MarketsandMarkets, there will be plenty of opportunity for designers of haptic applications. The firm projects that the haptic technology market will reach US$19.55 billion in value by 2022, representing a CAGR of 16.20% from 2016 to 2022. The research firm cites increasing adoption in consumer electronics and also the potential opportunities in medical and automotive application areas as key drivers for this growth. For designers, underlying technologies such as the MAX20303 PMIC can address the challenges of bringing the sense of touch to small, ultra-low-power electronic devices.