Wearable Technology: 3 Considerations for Super-Small Power Supply Solutions

From glasses and watches to fitness and sleep monitors, the latest wave of consumer products — featuring miniaturized wearable technology and the Internet of Things (IoT) — continues to demand smaller and more efficient power supply technologies than ever before.

System designers will get as much of the system functionality as possible into an ASIC, but there will always be a call to add more subsystems, from wired and wireless connectivity chipsets to novel product differentiation features. Adding features via additional chipsets after ASIC definition means supporting additional power supply rails. Furthermore, the tiny battery size used in wearable devices limits the total available energy, which means total system power efficiency is very critical to meeting consumer expectations for a long operating life.

Manufacturers of switching DC-DC buck converters have risen to the challenge by shrinking their parts to less than 1 mm through advances in chip scale packaging (CSP). The smallest such buck converter today measures 0.8 x 0.8 mm, thanks to a CSP package with bump pitches as small as 0.28 mm. In many products, the regulator device also includes internal MOSFETs, further minimizing the board space needed for power conversion.

But package size is only one factor wearable technology designers must consider to minimize the board space needed for power regulation. Here are three other key considerations.

  • Switching frequency: The complete power solution (assuming integrated MOSFETs) includes an inductor and two capacitors. By picking a regulator with a switching frequency of between 2 MHz and 6 MHz, designers can reduce the inductor capacity to less than 1 micro-Henry, shrinking the passive circuit elements and the active silicon.
  • Real-world power efficiency: Switching converters with operating frequencies of more than 1 MHz DC-DC present a tradeoff between efficiency and circuit size, since higher frequencies give up 1-2% efficiency. Today's switching converters offer up to 95% efficiency, so most often wearable device designers are willing to balance the efficiency/size tradeoff to get the smallest possible form factor. Another important factor is wearable devices stay on for extended periods (days or weeks). That requires processors to be put into low-power standby states. To extend battery life during standby states, many power converters use power save modes to reduce switching frequency, which saves additional power.
  • Programmable output: Changing voltages dynamically is a popular technique for conserving power by moving to a lower voltage during standby mode. With a buck converter that features digitally programmable Vout, there is no need for additional resistors that would ordinarily set the output voltage. This reduces the board space needed, along with the component count.

Wearables present board designers their biggest challenge ever in delivering the functionality people expect is such a limited space. But by following the tips above, designers can implement power solutions they need for key functionality while maintaining their form factors.

9 comments on “Wearable Technology: 3 Considerations for Super-Small Power Supply Solutions

  1. Davidled
    April 12, 2014

    Intel released Quark MCU to target wearable embedded application requiring small foot print and low power. This Chip could be used for medical industry, fitness and heath insurance. The below link provides more in detail:

  2. Netcrawl
    April 13, 2014

    Intels' challenge has been always about how to reduce power comnsumption, they hope that Quark could expand market Intel can go, Its Intel's fisrt major step into wearable space. But its going to be tough because they have plenty of competitors here- Qualcomm could be their biggest rival.

  3. Netcrawl
    April 13, 2014

    @Daej Intel's Atom chips can't match ARM muscles in the market, that's where Quark comes in, Intel is tasking Quark platform for covering markets that traditonally use embedded microprocessors and other types of low power controllers. 































  4. etnapowers
    April 15, 2014

    It will be a big challenge because the wearable technology holds big promises of becoming an high margin business and a wide range of diffusion among users for many purposes: fitness, medical,  safety etc…

  5. Victor Lorenzo
    April 16, 2014

    @DaeJ >> …Quark MCU

    It is hard for me to find a place for this SoC. It is too complex to integrate, requires too many different power supplies, requires too much PCB area for package and routing, consumes over 2W (theoretically) at only 400MHz, lacks several peripherals required for many wearable and/or embedded devices…

    I don't see how Intel's Quark processors could get even close to be able to compete with ARM's Cortex A-Series processor implementations like Qualcom's, Freescale's or even TI's (see Sitara processors like this

    Nevertheless Quark processors are a step forward.

  6. Sachin
    April 16, 2014

    The ultimate objective in the design of any item of wearable technology is the optimization of functionality and power efficiency so that the resultant device works better for longer. The first two factors mentioned in this article i.e. switching frequency and real-world power efficiency can both be achieved by careful and repetitive analysis while making the tradeoff between the board or circuit size and the eventual efficiency. I really love how you put this point across Andy.

  7. Sachin
    April 16, 2014

    Wearable technology, especially when it comes to devices and gadgets that function as IoT devices, is faced by many challenges but the one that really stands out (and indeed the one that is now giving most design engineers the real headache) is how to increase the power efficiency of the devices so that they can last and function for longer while at the same time trying to minimize the total board space on which the device is laid out. The above considerations should make the task a little easier though the headaches will still remain unless a new power source is developed soon.

  8. Davidled
    April 16, 2014

    Typically, the Intel Quark features integrated security and SW stacks for security and connection of Internet design. This chip is approximately 5 times smaller and 10 times lower in power than Atom Processor.  At least there is comparison for size and power consumption between Quark and Qualcomm.

  9. geek
    April 26, 2014

    Interesting post, Andy. Apart from efficient utilization of power, what do you think about alternate sources of charging when it comes to wearable technologies. Things like wireless charging and solar charging are being tested but are there any other ways you can think of or know about?

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