Maxim Integrated’s two new sensors were designed with next-generation wearables in mind, where small size and low power consumption are the paramount concerns. But in order to provide true value, these new wearable health and fitness monitors also offer high accuracy in measuring human biometrics such as body temperature and heart rate.
The MAX30208 Clinical-Grade Digital Temperature Sensor
This MAX30208 delivers clinical-grade temperature measurement accuracy (±0.1°C) and responds quickly changes in temperature. Designed for smartwatches and medical patches, it measures temperature at the top of the device and does not suffer from thermal self-heating, which can be a challenge for small devices, especially wearables.
Accuracy is within ±0.1°C from +30°C to +50°C and within ±0.15°C from 0°C to +70° C. The latter range, of course, is well beyond human physiological inputs but will be useful for IoT-based measurements.
Block diagram for the MAX30208. Image from Maxim Integrated
The unit includes a 32-word FIFO to store temperature data. High and low threshold voltages can be set with the additional functionality of an alarm that can be raised if these limits are exceeded. The MAX30208 employs a standard I2C serial interface to communicate with the host MCU.
The device operates from a power supply that can range from 1.7V to 3.6V and requires only 67μA during measurement, and 0.5μA during standby. This is one of Maxim's sticking points with this device, along with its tiny size, fitting into a 2mm x 2mm x 0.75mm 10-Pin thin LGA package.
The MAXM86161 In-Ear Heart Rate Monitor
The MAXM86161 heart rate monitor measures SpO2 (peripheral capillary oxygen saturation), a measurement of the amount of oxygen in the blood), as well as heart rate.
The device is essentially an optical data-acquisition system. The transmitter side has three programmable high-current LED drivers, while the receiver is based on a high-efficiency PIN photo-diode and an optical readout channel.
Block diagram for the MAXM86161. Image from Maxim Integrated
The optical readout channel includes an analog front-end (AFE), which eliminates the need for an external device to perform this function—another point Maxim highlights for comparison against competing systems.
Like the MAX30208, the MAXM86161 is also notable for its low power needs. It reportedly consumes only 67μA operating current during active conversion, half the power that the closest competing device requires at 135μA. It operates from a single supply voltage that can range from 3.0V to 5.5V.
The unit has an operating temperature range of -40°C to +85°C. It’s available in a 2.9mm x 4.3mm x 1.4mm OLGA package, which Maxim asserts is 40% smaller than the competition.
Eval Kits for Faster Time to Market
To enable OEMs to get their products to market ASAP, Maxim Integrated offers two evaluation systems for these devices:
There are many participants in the burgeoning field of wearable healthcare sensors, so designers have many choices to make. If a non-mobile device that plugs into wall current is being designed, the ultra-low-power figures that these Maxim devices sport will not be necessary. Additionally, not all applications will need the impressive accuracy that these units offer.
- Texas Instrument’s TMP117 is a temperature sensor that communicates via SMBus as well as via I2C interface. For medical applications, it meets ASTM E1112 and ISO 80601-2-56, yet is specified at ±0.3°C (maximum) from –55°C to +150°C.
- ROHM’s BH1790GLC is a heart rate monitor IC that can be used for wearable devices. It communicated via I2C, operates over a temperature range of -20°C to +85°C, and typically consumes 200μA.
Given the popularity of small, low-power wearable devices (and Maxim's notable emphasis on healthcare applications), these two new devices are certainly on-trend.
Have you ever designed a wearable? Tell us about the challenges you came across (and the methods you used to address them) in the comments below.