Enabling Seamless Transition to Sensirion’s SHT4x Family of Sensors

Symmetry Electronics in Blogs on January 24, 2024

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Established in 1998, Symmetry Electronics, a Division of Braemac, is a global distributor of electronic components and systems. Combining premier components and comprehensive value-added services with an expert in-house engineering team, Symmetry supports engineers in the design, development, and deployment of a broad range of connected technologies.

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It has recently been announced that the STMicroelectronics (ST) HTS221 capacitive digital sensor for relative humidity and temperature is in the process of being terminated. In light of the EOL, ST and Sensirion have collaborated to coordinate a transition guide that positions Sensirion’s SHT4x sensor family as a comprehensive drop-in replacement for the HTS221.

Replacing HTS221 with SHT4x Solutions

As a high-quality alternative solution for the HTS221, the SHT4x sensor family is also designed to provide ultra-precise temperature accuracy of +-0.2°C and humidity accuracy of +-1.8%. Additionally, the SHT4x family features:

VDD = 1.08V ... 3.6V
average current 0.4uA (@ 1 meas/s)
I²C interface
operating range: 0...100%RH, -40...125°C
NIST traceability
optional protection membranes and foils
Powerful on-chip heater that can be used for self-decontamination

While SHT4x solutions are drop-in replacements, there are key differences (Figure 1) between the two products that developers need to consider.

Figure 1: Key differences between the HTS221 and the SHT4x.

Source: STMicroelectronics

Additionally, there are package design differences between the two products. The SHT4x comes in an open-cavity dual flat no-lead (DFN) package (Figure 2), where the sensor opening is centered on the top side of the package.

Figure 2: Packaging design differences between the HTS221 and SHT4x

Source: STMicroelectronics

Compatibilities

The HTS221 and SHT4x sensors use the I²C protocol with addresses 0xBE and 0x44, respectively. To communicate with the SHT4x, send its 7-bit I²C address with an additional bit for the operation type: 'zero' for write, 'one' for read. The SHT4x features a heater for pre-measurement cleaning, controlled via I²C commands. It offers three sensor measurement repeatability modes: Low (1.3-1.6 ms), Medium (3.7-4.5 ms), and High (6.9-8.3 ms), balancing measurement accuracy and energy consumption. The heater has two durations: long pulse (0.9-1.1 s) and short pulse (0.09-0.11 s), both self-deactivating.

SHT4x Solutions Available Now at Symmetry Electronics

For developers seeking a smooth transition, SHT4x solutions are readily available through Symmetry Electronics. This collaboration between ST and Sensirion ensures a reliable supply chain for the SHT4x family, offering a seamless migration path for those transitioning from the HTS221. Symmetry Electronics stands as a trusted source for acquiring these cutting-edge sensors, enabling a swift and efficient upgrade process.