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Non-contact thermometer design to tackle Covid-19

Non-contact thermometer design to tackle Covid-19

Technology News |
By Nick Flaherty






With the rapid spread of Covid-19 around the world, non-contact thermometers are becoming a medical necessity. Detecting viral and bacterial infections require precise body temperature measurements, preferably without contact, so medical personnel can help prevent the spread of disease within the healthcare system. According a report by Research and Markets, globally, the non-contact thermometer business outlook is expected to increase at a CAGR of over 11% from 2018-2024 says Abigail Sun, Senior Application Engineer at Renesas Electronics.

This growth in non-contact thermometers is expected primarily in North America and APAC, but all regions are expected to see an increase. The reason for this growth is an aging population that is most susceptible to infections, she said.

The IR Contactless Thermometer is based around the RL78/H1D microcontroller which integrates a 24bit Delta-Sigma A/D converter, SAR A/D converter, programmable gain amplifiers, an operational amplifier, and an 8-bit/12-bit D/A converter. It also has a built-in LCD controller/driver, which makes the RL78/H1D well suited for healthcare devices. This lower power consumption and heavy integration within one MCU allows the system to have a longer battery life and smaller solution size. Moreover, the RL78/H1D has a wide input range of 2.7V to 5.5V. This makes the RL78/H1D a better fit in battery applications. The RL78 also provides an option of a 64pin 4x4mm TFBGA package, allowing for a compact board design.

To manage the power supply for the whole system, the design uses the ISL9021A low IQ, low noise and high PSRR LDOs, which is the best fit for battery applications. Its input voltage range is between 1.5V to 5.5V and the output voltage comes in many fixed voltage options, with ±1.8% accuracy over-temperature, and line and load ranges. The ISL9021A has a typical PSRR of 75dB at 10kHz and 50dB at 1MHz, which enables the LCD in the system to get low noise and stable power. It is also offered in tiny 4-bump 0.975mmx1.155mm WLCSP and 1.6mmx1.6mm 6 Ld µTDFN packages. This makes it well suited for small board development in battery-powered handheld devices.

The battery charging portion of the thermometer design is based around the ISL9205D, an integrated single-cell, Li-Ion or Li-polymer charger. This operates as a linear charger when the AC adapter is a voltage source. The battery is charged in a standard Li-Ion charge profile, that is, a constant current phase followed by a constant voltage phase (CC/CV). When the adapter output is a current-limited voltage source and the current limit is smaller than the programmed constant current of the IC, they will operate as a pulse charger, where the charge current is determined by the current limit of the AC adapter during the constant current phase. The ISL9205D operates in a linear mode during the constant voltage phase in both adapter cases. It is also offered in 3x3mm QFN or DFN packages, making it small enough to fit into medical solutions.

A range of technology designs for Covid-19 is at www.renesas.com

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