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Pressure-Sensing Solution for EV Braking, Transmission, HVAC Cuts Design Time

Oct. 12, 2021
The RAA2S425x ICs developed by Renesas integrate digital and analog functionality that also keeps system bill-of-materials and production costs low, including digital calibration to eliminate trimming of sensing elements.

From safety features to reducing pollution and optimizing engine efficiency, many of the critical systems in a vehicle rely on pressure sensors. To manage these systems, Renesas Electronics introduced the RAA2S425x family of ICs. The new devices are said to provide accurate amplification and sensor-specific correction of signals in automotive battery electric vehicles (BEVs), plug-in hybrid electric vehicles (PHEVs), and fuel-cell electric vehicles (FCEVs) for pressure-sensing braking, transmission, and HVAC systems.

The RAA2S425x ICs feature digital and analog functionality that Renesas says reduces customers’ system bill-of-materials (BOM) and production costs. Digital calibration helps keep assembly cost low by eliminating the trimming of sensing elements by external devices or lasers.

The ICs integrate a 16-bit embedded RISC microcontroller that provides digital compensation of offset, sensitivity, temperature drift, and nonlinearity. A non-volatile memory (NVM) is used to store calibration coefficients and configuration data in automotive environments enduring high temperatures, humidity, dust, vibration, and electrical noise, all of which is reduced since the RAA2S425x series communicates digitally with calibration equipment.

Measured values are provided via a ratiometric analog output signal and output update rates are 100 μs in the fastest mode. Ratiometric techniques describe an output signal that changes in proportion to an alteration in input or supply voltage.

The product family integrates overvoltage and reverse-polarity protection circuitry, ASIL-B compliance according to ISO26262, and electromagnetic compatibility.

Sensor compensation has historically been based on an analog architecture. The RAA2S425x ICs support all major pressure-sensing technologies and feature an analog front-end (AFE) for enhanced signal conditioning. Their extended analog sensor offset compensation (XSOC) is said to be adjustable to nearly all resistive bridges. The sensor offset correction uses XSOC and digital zooming with up to 18-bit resolution.

Selectable on-chip PTAT (proportional to the absolute temperature) support is employed for external temperature sensing. The RAA2S425x ICs deliver pressure and temperature readings with accuracy (0.35% to 1.0%) over a wide temperature range (−40 to 150°C), according to Renesas.

Chip Deep Dive

Let’s look at one example of the RAA2S425x family. The AEC-Q100 Grade 0 qualified RAA2S4251B is designed for amplification and sensor-specific correction of differential bridge sensor signals. Featuring a maximum analog preamplification of 900 with XSOC, the part is said to be adjustable to nearly all resistive bridges.

Conditioning calculation is accomplished via a 16-bit RISC microcontroller. Calibration coefficients and configuration data are stored in the NVM. The RAA2S4251B is optimized for automotive environments—it has overvoltage and reverse-polarity protection of ±40 V, according to Renesas. RAA2S4251B has the ability to cover large sensor span and high accuracy over the entire temperature range. End-of-line calibration is supported through an output pin via a one-wire interface (OWI).

Renesas notes that engineers can combine the RAA2S425x solution with complementary MCU, analog, and power offerings for automotive pressure-sensing braking, transmission, and HVAC systems.

The RAA2S425x devices, available now, are housed in 4- × 4-mm QFN-24 packages with wettable flanks.

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