The Internet of Things is already a hot topic for 2015, promising to deliver internet connectivity to such humble consumer items as the refrigerator and the wristwatch. For wearables in particular, IoT poses some challenges for the power management designer.
Why? Well, when you're talking about a wearable IoT device such as a watch, you're talking about multiple functions, small size, light weight, WiFi and perhaps Bluetooth, and minimum power consumption - conflicting requirements that have traditionally made uneasy bedfellows.
Wearable fashion for the connected woman: the MICA bracelet from Opening Ceremony & Intel.
For example, the Samsung Gear S, announced in November, allows users to get online at 3G speeds, make calls and send messages. Sensors include an accelerometer, gyroscope, compass, heart rate monitor, ambient light sensor, UV sensor, and barometer.
All that goodness demands some serious processing power - for the Gear S, an ARM-based dual-core Exynos 4212 processor running at 1.0 GHz with 512 megs of RAM and 4 GB internal memory. Plus a 300 mAh Li-ion battery to keep the lights on. Not a lot compared to the 2400mAh battery in my Galaxy S4, but it does give you a day or so of use between charges.
Needless to say, when it comes to the overall portable market, improved battery life is the top must-have for consumers. Sadly, progress in this area has been, shall we say, glacial. No Moore's law for batteries.
While we're waiting impatiently for the Next Big Thing in battery technology, though, the drive towards smaller and higher-function devices is driving innovations in power management across a number of other areas, including battery charging and energy harvesting.
A number of suppliers have introduced battery charger solutions aimed at wearable electronics.
TI has a range of power products aimed at the wearable space, including traditional and wireless chargers, and nano-power harvesting ICs.
The MAX1467 & MAX14676A Wearable Charge Management solutions from Maxim have the ModelGauge fuel gauge that provides an estimate of the available capacity for rechargeable lithium batteries.
And this week, Freescale announced its BC3770 battery charger, which can be powered from USB, and offers 2A charging capability and a choice of charging profiles, all programmable via an IIC interface.
As power levels decrease, energy harvesting - reclaiming otherwise wasted energy to extend battery life - becomes a viable option. Some of the options that are being looked at utilize light, heat, movement, or even biological reactions.
For example, a thermoelectric generator transforms heat into energy using the Seeback Effect, in which a current is generated by a junction of two different metals with a temperature difference between them. And a piezoelectric device accumulates electrical charge as a result of mechanical stress or movement.
Even if harvested energy can't replace a battery completely, it can augment the energy available and hence extend battery life. For example, a 2 cm 2 solar cell added to a wearable device can give up to a 7% improvement in outdoor use.