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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MAX-ECG-MONITOR and MAX-HEALTH-BAND Demo – electronica 2018
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Introducing the Health Sensor Platform 2.0 (MAXREFDES101)
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Introduction to the MAX20327 12V Capable, Low-RON, Beyond-the-Rails DPDT Analog Switches
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Wristband Health Monitoring Demo with MAX86141
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Introduction to the MAX20326 Dual Precision Bus Accelerator
Fit Two Shirt: A Wearable Wellness Platform Example
Introduction to the MAX17262 5.2µA 1-Cell Fuel Gauge with ModelGauge m5 EZ and Internal Current Sensing
Introduction to the MAX17303 MAX17313 1-Cell ModelGauge m5 EZ Fuel Gauge with Protector
Introduction to the MAX31341B Low-Current, Real-Time Clock with I2C Interface and Power Management
Introduction to the MAX16142 nanoPower, Tiny Supervisor with Manual Reset Input
Heart Rate Monitor Demo
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Introduction to the MAX16150 Nano-Power Pushbutton ON/OFF Controller and Battery Freshness Seal
Introduction to the MAX32664 Ultra-Low Power Biometric Sensor Hub
Wearable Fitness/Medical and IoT Power Demo - electronica 2018
Introduction to the MAX14745 and MAX20335 PMICs with Ultra Low IQ Voltage Regulators and Battery Charger for Small Lithium Ion Systems
Introduction to the MAX86171 Best-in-Class Optical Pulse Oximeter and Heart-Rate Sensor AFE for Wearable Health
Introduction to the MAX30131 MAX30132 MAX30134 4-Channel Ultra-low Power Electrochemical Sensor AFE
Introduction to the MAX20353 Wearable Charge Management Solution
Introduction to the MAX16158 Nanopower, Tiny Supervisor with Manual Reset Input
Introduction to the MAX86916 Integrated Optical Sensor Module for Mobile Health