IN Brief:
- The MLX90636 measures 1.8 × 1.8 × 0.75 mm and is intended for compact health-monitoring electronics.
- Melexis specifies ±0.2°C accuracy across the human body temperature range, with programmable sampling from 0.5 to 32 Hz.
- Wrist-based core temperature estimation remains under research and has not been established as a validated capability of the sensor alone.
Melexis has introduced the MLX90636, a miniature infrared temperature sensor intended for smartwatches, fitness bands, smart rings, and other compact electronic devices requiring contactless thermal measurement.
The device measures 1.8 × 1.8 × 0.75 mm and provides factory-calibrated temperature sensing with a specified accuracy of ±0.2°C across the human body temperature range. Its compact surface-mount package is designed to support integration into equipment where circuit-board space, power consumption, and thermal stability impose significant restrictions on component selection.
Melexis is also investigating the use of the sensor to estimate core body temperature from measurements taken at the wrist. That work remains at the research stage, with the company developing an evaluation platform for feasibility studies rather than offering a completed core temperature measurement system.
The MLX90636 operates using far infrared sensing, detecting thermal radiation emitted by the surface within its field of view. The sensing element converts the received energy into an electrical measurement, which is processed using calibration information and compensation for the sensor's operating conditions.
Unlike a contact thermometer, an infrared sensor does not require a direct conductive thermal path between the measured surface and its sensing element. Its reading nevertheless depends on the optical arrangement and the thermal environment, because the detected radiation must be interpreted in relation to the target and surrounding conditions.
Miniaturisation makes this task more demanding. Electronic components close to the sensing element can generate heat, while the temperature of the package and circuit board may change during operation. These effects can influence the measurement unless the sensor's thermal behaviour is understood and appropriately compensated.
Melexis has designed the MLX90636 to resist rapid ambient temperature variations and air turbulence, both of which can disturb infrared measurement conditions. The company identifies thermal compensation as an important part of maintaining measurement stability within the restricted dimensions of wearable equipment.
The sensor uses a five-terminal land grid array package and incorporates factory calibration information stored in non-volatile memory. These constants support temperature calculation without requiring each device to undergo a complete independent calibration procedure during ordinary product assembly.
An integrated post-calibration function provides additional adjustment options after installation. This can be relevant when mechanical integration, optical positioning, or the surrounding thermal arrangement introduces differences between a laboratory measurement and the final product configuration.
Communication takes place through an I²C interface, with the device supporting 1.2 V or 1.8 V bus voltage levels. Its operating supply can be configured for 2.8 V or 3.3 V, allowing integration with different embedded power arrangements and host processors.
The I²C address can be configured in software, providing flexibility when the sensor is connected to a system containing other digital peripherals. The manufacturer also supplies software driver resources intended to support integration and application development.
Measurement refresh rates are programmable from 0.5 to 32 Hz. A lower setting allows less frequent temperature sampling, which may be suitable for measurements that change slowly, while higher rates provide more frequent updates when the application requires them.
Sampling frequency affects the energy budget of the sensing function, but the battery life of the complete product depends on considerably more than the infrared device. Host processor activity, communications, displays, other sensors, and power management behaviour can dominate the total consumption of a wearable system.
Melexis describes the sensor as having microampere-level sleep current. Its November announcement and product specification page publish different numerical upper limits, so the final operating budget should be established against the applicable device datasheet and the conditions under which the current is measured.
The MLX90636 provides a nominal 50-degree field of view, making optical positioning an important part of the mechanical design. The surfaces contributing to a measurement depend on the orientation of the device, the separation from the target, and the geometry of the surrounding enclosure.
In a wrist-worn device, changes in fit and positioning can alter the relationship between the sensor and the skin. Measurements may consequently be affected by movement, local thermal conditions, and the structure of the wearable even when the semiconductor itself is operating within its specified limits.
The manufacturer references ASTM E1965-98 in support of its stated temperature accuracy. That specification concerns infrared thermometry under defined measurement conditions; it does not establish that an integrated wearable device can directly determine internal body temperature to the same accuracy.
Core body temperature is distinct from temperature measured at the skin surface. The relationship between the two changes according to local blood circulation, ambient temperature, physical activity, and heat exchange between the body and its surroundings.
A wearable system attempting to estimate core temperature must therefore interpret the skin measurement alongside an appropriate physiological or computational model. Additional information may be necessary to account for variations in the thermal relationship between the measurement location and the body's internal temperature.
Melexis is researching wrist-to-core modelling as part of its wider development programme. The company has not published a completed, clinically validated estimation method or quantified its accuracy across the range of users and operating conditions that a commercial wearable would encounter.
To support this research, Melexis is finalising an evaluation kit intended for feasibility studies. The company is inviting potential customers to investigate whether the sensing hardware can contribute to core temperature estimation within their particular devices.
The MLX90636 itself is commercially available. Its immediate capabilities are miniature, calibrated infrared temperature measurement, configurable digital interfacing, and low-power operation, with the suitability of any individual application dependent on system integration and measurement validation.
Further research will determine whether algorithms using wrist measurements can provide reliable estimates of core body temperature. Until those results are established, the sensor's specified ±0.2°C accuracy should remain separate from claims about the accuracy of a complete wearable health-monitoring system.
