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Mems pressure sensor shuns soap and shampoo for wearables


Called LPS33W, the IPx8-rated device is protected by an internal viscous potting gel, and is claimed to withstand: “salt water, chlorine, bromine, detergents such as hand soap and shampoo, e-liquids, and light industrial chemicals such as n-pentane,” said ST.

The package is cylindrical (3.3mm diameter x 2.9mm), and shaped, to ease the use of O-rings when a sealed enclosure is needed, and the lid is corrosion resistant.

According to the firm, the gel is a proprietary formula, and its properties, together with the built-in signal-conditioning asic, achieve 0.008hPa RMS pressure noise.

“Susceptibility to re-flow soldering stress during assembly is also extremely low, drifting less than ±2hPa and recovering normal accuracy in 72 hours,” said ST. “Temperature compensation keeps accuracy within ±3hPa over the operating range from 0°C to 65°C.”

STM-LPS33W-MEMS-pressure-sensorGel composition is a bit is a mystery, with only mechanical properties provided in the data sheet (Table 9)

Factory trimming values are stored in a non-volatile structure, and are downloaded into registers at switch-on for normal operation. No further calibration is required.

Consumption is 15µA in ‘high-performance’, 3µA in low-power mode and 1µA when shut-down.

A 128-bit FIFO stores up to 40 slots of 32bit pressure and temperature data, reducing the frequency of host MCU interactions, allowing the host to sleep more and save power.

Supply is 1.7 to 3.6V, and I2C and SPI digital interfaces are built-in, as is a low-pass filter.

Mass production has started.