Monday, June 17, 2024

IR Contactless Thermometer Reference Design

The IR contactless thermometer design includes a microcontroller, a lithium-ion battery charger, and a low dropout regulator, which are suitable for healthcare applications.

Block Diagram
Block Diagram

Infrared (IR) contactless thermometers represent a safe and efficient method for temperature measurement. These devices, which do not require skin contact, offer the advantage of swiftly and accurately determining temperature, provided they are used within the specified range and close to the forehead. With the emergence of new viruses, the demand for such contactless thermometers has surged significantly.

The IR contactless thermometer reference design by Renesas features a combination of critical components: the RL78/H1D, a microcontroller unit (MCU), the ISL9205D, a Lithium-ion battery charger, and the ISL9021A, a Low Dropout Regulator (LDO). This integration of technologies provides a comprehensive solution for developing IR contactless thermometers.

The RL78/H1D is outfitted with sophisticated high-precision analogue components, such as a Delta-Sigma Analog-to-Digital Converter (ADC), Successive Approximation Register (SAR) ADC, Programmable Gain Amplifier (PGA), and Operational Amplifier (OPA). These features are crucial for delivering precise and swift measurements. It also includes an integrated Liquid Crystal Display (LCD) controller/driver, making the RL78/H1D a perfect fit for Infrared (IR) contactless thermometer applications. In contrast, the ISL9205D is a cost-effective, fully integrated charger designed explicitly for single-cell Lithium-ion (Li-ion) batteries, capable of handling high input voltages. A high-performance LDO further boosts The design’s effectiveness, which guarantees a stable and reliable power system.

At its core is the high-precision analogue MCU, which serves multiple functions: it amplifies signals, manages system control, and drives an LCD, all within a single chip. Complementing this, integrating a high-performance charger and LDO, capable of handling high input voltages, provides a comprehensive and efficient solution. This combination of features enhances overall system performance and efficiency.

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The MCU employed in this design is tailored explicitly for sensing transducers in healthcare devices, with an optimization focus on blood pressure monitors. This makes it highly suitable for critical healthcare applications and devices. It supports a voltage range of 1.8V to 5.5V. Memory-wise, it boasts up to 8KB of SRAM and 128KB of Program Flash. The on-chip oscillator frequencies are diverse, with high-speed options ranging from 1 to 24 MHz and a low-speed option at 15kHz. Additional features include an RTC, power-on reset, and low voltage detection.

The lithium-ion battery charger features Thermaguard, a safety mechanism against overheating. Should the IC’s die temperature exceed +100°C, a thermal foldback function reduces the charge current to mitigate further temperature increase. Additionally, the ISL9205 provides external temperature monitoring using a Negative Temperature Coefficient (NTC) thermistor to monitor the battery or ambient temperature.

Renesas has tested this reference design. It comes with a Bill of Material (BOM), block diagram, etc. You can find additional data about the reference design on the company’s website. To read more about this reference design, click here.

Nidhi Agarwal
Nidhi Agarwal
Nidhi Agarwal is a journalist at EFY. She is an Electronics and Communication Engineer with over five years of academic experience. Her expertise lies in working with development boards and IoT cloud. She enjoys writing as it enables her to share her knowledge and insights related to electronics, with like-minded techies.

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