Advances in low power microcontrollers and communication ICs have made it possible to build lightweight, unobtrusive, wearable smart devices that run diverse applications. Popular examples include smart watches and body signal monitoring bands.
Power and Battery Management
In a wearable device the power system must be able to regulate voltage from a battery—a voltage source with a declining voltage output. The regulators must be very efficient so as to maximize charge usage, and must also supply the number of rails required by the design. The usable voltage range of a rechargeable Li+ battery ranges from 4.2V to approximately 3.2V. Most wearable products use main power rails that are below the minimum charge of a single-cell Li+ battery, so the main rails within a wearable design are sourced from a step-down regulator. Some functions within a wearable product might require a higher voltage level than is provided by a single-cell battery. To provide these voltage levels the power management function must contain at least one step-up regulator. The number of rails required depends on the device functionality, but for optimum efficiency it’s best to minimize the number of required rails.
Power usage and processing capabilities are the most important selection criteria for a microcontroller for wearable applications. A system partitioning strategy should be used to decide which system functions are best integrated into the microcontroller and which can be handled externally. Because the wearable health devices read body signals, the capabilities of any on-chip analog circuitry must also be taken into account to ensure they can accurately process low-level body signals.
Sensors and Sensor Interface
The electrical outputs from body sensors have very low magnitude, in the millivolt and microvolt range. Accordingly, many of the sensors that are practical for wearable health applications have been combined with amplification and conversion circuits within a single die or package so that they output either a higher level analog signal or a serialized digital signal.
Wearable Charge Management SolutionMAX14676
This battery-charge-management solution includes a linear battery-charger with 28V tolerant input, smart power control, and several power-optimized peripherals. A boost regulator with 5V to 17V output, and 3 programmable current sinks can drive a variety of LED configurations.
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ModelGauge m3 Fuel GaugeMAX17047/MAX17050
These battery fuel gauges provide excellent short-term and long-term accuracy by using both coulomb counting and voltage-based ModelGauge algorithms. ModelGauge m3 cancels offset accumulation error in the coulomb counter while providing better short-term accuracy than any purely voltage-based fuel gauge.
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USB/AC Adapter, Li+ Linear Battery ChargerMAX8606
This complete 1-cell Li+ battery charge-management IC operates from either a USB port or AC adapter. It integrates a battery disconnect switch, current-sense circuit, PMOS pass element, and thermal-regulation circuitry, while eliminating the external reverse-blocking Schottky diode, to create a simple and small charging solution.
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Stand-Alone ModelGauge m5 Fuel Gauge with SHA-256 AuthenticationMAX17201/5/11/15
This ultra-low power fuel gauge IC with SHA-256 authentication doesn’t require characterization, ideal for pack-side implementation.
28V Internal Switch LCD Bias Supply with True ShutdownMAX1606
Boost converter uses internal switches to deliver up to 28V from inputs as low as 0.8V, with True Shutdown™.
30V Internal Switch LCD Bias SupplyMAX1605
Boost converter with 0.5A internal switch in a tiny 6-pin SOT23 package, accepts inputs as low as 0.8V.
For information about designing wearable health products, including example block diagrams of typical wearable products, please visit:
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