TI gives you tips! How to quickly design an infrared body temperature detector?

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TI gives you tips! How to quickly design an infrared body temperature detector? [Copy link]

Temperature detection is a necessary monitoring when we are at home, in and out of the community or workplace, and when traveling. Infrared thermometers help reduce contact transmission through non-contact temperature measurement. Here we will talk to you about this system and the main design solutions.
The MSP430 series of microcontrollers is a 16-bit ultra-low power RISC mixed signal processor that Texas Instruments (TI) began to market in 1996. There are countless applications developed based on this series of products, especially for sensing and detection terminal applications. Because it integrates high-performance ADC, LCD driver, serial communication, PWM output and other modules on the chip, it has become the only choice for infrared thermometer manufacturers. With the rich online software and hardware design resources provided by TI, developers can greatly simplify the design process, quickly develop infrared thermometer prototypes, and save circuit board space to reduce costs.
The figure below provides an infrared temperature detector system solution based on the MSP430 microcontroller and TI power management, amplifier and temperature sensor devices.

Figure 1 Infrared body temperature detector system block diagram
The MSP430 series microcontroller, as the main control MCU of the solution, can provide the following functions and features for the thermometer system design:
Rich peripherals meet the design requirements of the thermometer:
1. The successive approximation SAR ADC or high-resolution Sigma-Delta ADC integrated on the MSP430 chip cooperates with TI's TLV333 amplifier to sample the high-precision signal collected by the analog infrared temperature sensor and convert it into digital temperature. At the same time, it can monitor the battery voltage in real time;
2. The LCD driver module integrated on the MSP430 chip can help developers quickly implement the LCD display design for the thermometer. The MSP430FR4133 has a built-in LCD driver module with up to 4×36 or 8×32 segments, which supports flexible configuration of LCD segments and COM pins, simplifying the PCB design of developers;
3. The I2C serial communication interface can meet the signal acquisition and input of auxiliary sensor elements such as high-precision digital temperature sensors or digital infrared temperature sensors, digital proximity sensors, etc.;
4. The on-chip integrated timer module can output multiple PWM signals to drive thermometer indicators, buzzers and other devices;
5. The interrupt enable of GPIO in ultra-low power mode can provide fast key response in standby mode for battery-powered thermometer systems.
Ultra-low power design helps the thermometer to have a long battery life and high frequency of use:
Since its launch in 1996, the MSP430 series of microcontrollers has always used ultra-low power consumption as the family gene of the product, providing a wealth of low-power intelligent peripherals for the product's low-power design. Because of the high frequency of use, infrared thermometers have high requirements for the battery life and frequency of use of the device, so the low power operation of the thermometer becomes a key challenge in system design. The
rich product series provides flexible memory options:
The MSP430 series of microcontrollers provide more than 16KB of on-chip memory to meet the memory requirements of most thermometer products. The rich product family of this series provides a variety of memory options up to 512KB. Users can quickly migrate existing designs without too much work while choosing different memory sizes. The recommended product models for thermometers are:

Table 1 Recommended infrared thermometer MCU product models
The solution in Figure 1 also includes TI's rich power management, signal chain and sensor products.
The TPS61099 series chips are boost chips specifically designed for applications that require ultra-low power consumption. First, the static power consumption is only 800nA, and the input voltage is as low as 0.7V, which can perfectly support single-cell battery power supply. At the same time, it can achieve 80% efficiency under the conditions of input 1.5V and output 3.3V/10uA. The TPS61099x series chips provide two types of adjustable output versions and fixed output versions for customers to choose from. The fixed version supports almost all common output voltages from 1.8V to 5.0V.
The TPS62170 buck converter provides low IQ, which helps to extend the battery life of the system, especially when the system is not in use. In addition, it also supports high efficiency at switching frequencies above 2 MHz to help designers reduce the size of the required inductor, thereby reducing the size of the entire solution. The
TLV333 op amp is TI's zero-drift op amp series, which has the characteristics of high precision and low power consumption. On the one hand, the op amp's ultra-low input offset voltage (15 V max) and low temperature drift (0.02) help minimize temperature sensing errors, and its rail-to-rail input/output performance helps maximize the dynamic range. On the other hand, the low quiescent current (28 A max), low voltage (1.8V to 5.5V) and small package size (smallest SC70 package), plus the operating temperature range, are very suitable for handheld or battery-powered medical equipment. In addition, this op amp series also has dual-channel (TLV2333) and quad-channel (TLV4333) options.
Faster settling time and lower noise may be required in some systems to help speed up temperature measurement. For these cases, the OPA388 is a good choice to replace the TLV333. The OPA388 will provide lower input offset voltage (5μV maximum), lower noise (7 nV/rt(Hz)) and faster settling time (2μs), all of which will help minimize the settling time and the number of average samples required to achieve the specified temperature resolution.
TI has a variety of op amps that can be used to interface the signal between the analog sensing element and the ADC. The following table lists other amplifiers that could be suitable for this design, all of which are available in dual packages.

Table 2 Recommended op amps for signal interface
TI offers a variety of temperature sensors, and our high-precision digital sensor TMP117x has an accuracy of ±0.1°C over the range of -20°C to 50°C. The device integrates a 16-bit resolution ADC and can communicate with the designer's digital controller via I2C or SMBus. The device is designed for battery-powered systems because it has only 150nA Iq consumption in shutdown and only requires 3.5A per 1Hz conversion cycle. For systems with an integrated ADC in the MCU, TI also offers analog temperature sensors and thermistors. The LMT70 provides a voltage output corresponding to temperature with a maximum accuracy of ±0.13°C between 20°C and 42°C. For cost-sensitive systems, the TMP61 linear thermistor provides a 1% temperature tolerance and simplifies the calibration process using traditional NTCs. For more cost-sensitive digital temperature sensing applications, TI's TMP1075 can be used, which has an accuracy of ±1°C (maximum) over the range of 25°C to +100°C. For systems with an ADC integrated in an MCU, TI also offers analog temperature sensors. The TMP23x provides a wide range of design flexibility, as designers can choose from a range of accuracy and gain from ±0.5°C to ±6°C.
To power the ADC and sensing elements, designs often require a low-noise, sensitive voltage rail. Low-dropout regulators (LDOs) are a common choice because they are easy to use and able to provide clean, low-noise power to sensitive analog power rails. For this specific need, the TPS7A20's ultra-low noise (6 VRMS), high ripple rejection (85db @ 1 kHz), and low quiescent current (6 A typical, 150nA in shutdown mode) make it an excellent choice. This provides the required low-noise rails for the ADC and sensing elements (while filtering the DC/DC ripple and generating very little inherent output noise), while also providing low quiescent current for battery-powered applications (extending battery life). For battery-powered systems, the TPS7A02 is another good choice because it provides nanowatt-level IQ (25nA, 3nA in shutdown mode) while also providing high PSRR for post-DC/DC regulation. The TPS7A02 also has excellent transient response, which is critical for duty-cycle loads.
Some high-end products on the market also include low-power Bluetooth (BLE) communication modules. If you are interested in adding it to your system, the CC2640R2F IC or CC2650MODA module is a good fit. TI's SimpleLink software can help designers complete the development process as quickly as possible.
To reduce current consumption, you can also use load switches with integrated faults such as the TPS2051x, or the TPS22916xx with ultra-low leakage current, which can be used to disconnect the BLE module from the battery power supply or any other DC power supply. This can extend the battery life of the product while adding other features to the user.
The TI devices detailed in this article will help designers quickly design infrared thermometers. TI highly values our customers' work in designing and manufacturing this end equipment with the support of our global manufacturing base, while continuing to provide high-quality design assistance and excellent customer support.