FEAT RE FEA ATURE
COVER
COVER STOR Y
LOW POWER CONV ERSIO N I N HEALTH AND WELLBEING WEARABLE TECHNOLOGY
LOW POWER CONVERSION IN HEALTH AND WELLBEING WEARABLE TECHNOLOGY
Steve Knoth, senior product marketing engineer of power products at Analog Devices’ Power by Line ar Group explores ho w the latest ultra-l
solvi g key pow r i sues assosiated with the modern era of wearable devices
io-stats are vital signs that measure the human body’s basic functions. These include body temperature, pulse/ heart rate, respiratory rate and blood pressure. These are critical because an adverse change in vital(s) may indicate a decline in health, and vice-versa. Hospitals and doctor’s offices are
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obviously well-equipped with expensive devices to measure these bio-stats. But, imagine how much more quality-of-life could be improved if these bio-stats could be efficiently and inexpensively measured outside the medical arena. For example, in the home or at work, lifestyle and behaviour modifications could be made real time “on-the-fly”, improving health and possibly extending or even saving lives. ,
Fortunately a combina tion of device cost reductions and advanced sensor technology has improved to the point where the proliferation of medical and wellness smart wearables is increasing. These include simpler “single vital sign” units that attach to the body, to more sophisticated full-body sensor-filled
partitioning and efficientl circuit (IC) electronics sta exo-skeletons. But, from
these types of wearable s an integrated
is not trivial. To y powering ndpoint,
further understand this, let’s take a look “under the hood” of a typical smart wearable device .
POWERING SMART WEARABLES What makes a typical smart wearable device function? Well, one could think of it as a miniature embedded system. A wearable unit’s primary design goals are usually to have a compact form factor, low weight for wearability/ comfort and possess ultralow energy consumption to extend battery run time/life. However, powering these devices efficiently and accurately with minimal current draw is not so simple. Some of the key issues associated with powering smart wearables include the following:
POWERING SMAR WEARABLES 12 12 DECEMBER JANUAR 2018 ECEMBER/JANUARY 2018 || ELEC RO ELECTRONICS CS
Steve Knoth, senior product marketi g engineer of power products at Analog Devices’ Power by Linear Group explores how the latest ultra-low quiescent current IC solutions are solving key power issues assosiated w th the m dern era of w arabl
quiescent current IC solutions ar e devices
since output currents can be high, an LDO post-regulated switching regulator or a low-ripple switching regulator are an excellent choice
4) Processor power (the “brains” of the wearable). From ARM Cortex MCUs, DSPs, GPS chips or FPGAs need a
variety of low-voltage rails, spanning a gamut of currents. These can be
powered by LDOs or switching regulators 5) Since not all wearable devices are powered with rechargeable batteries – some may utilise primary cell (non- rechargeable) batteries that need to have long run times between
replacements. Therefore, finding a way to estimate battery run time is key 6) Compact size and low weight make the wearable device more comfortable for the user ICs in compact package s provide small solution footprints, thus enabling the device to have both offered in a small form factor and b e light weight
.
1) Low current consumption from the power management IC in a battery- powered device is paramount for increased run time. A micropower or a nanopower conversion IC is necessary 2) A MEMS sensor requires power from a quiet regulated power source. Busy actuators may also benefit. An LDO or low-ripple switching regulator is ideal for such rails since they have low output noise
3) Bluetooth/RF/Wi-Fi/cellular
connectivity system rails also require low noise. A low dropout regulator or,
Figure 1: L
Figure 1: LTC3388-1/-3 typical application circuit
LTC33 8-1/-3 ypical application circuit
ULT SOL
UL
LTRA-LOW QUIESCEN CURREN IC SOLUTIONSIONS
OW QUIESCENT CURRENT IC
It is clear that an IC solution that solves a wearables application needs, as well as the associated issues already discussed, should have the following attributes: Ultra-low quiescent current, both in operating mode and shutdown Wide input voltage accommodate a va
riety of power sources range to
The ability to efficiently power system rails (some with hi Capability to accur
without significantly affecting CI
ately count coulombs gher voltages >5V)
Figure 1: Tr
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ELECTRONICS
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