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New Bosch MEMS acceleration sensors Fifth generation of sensitive crash detectors SMA58x and SMA59x in SOIC14n housing

8th October 2012

Robert Bosch GmbH

ES Admin

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Bosch has introduced the next generation of peripheral acceleration sensors for passenger protection systems in vehicles – the fifth since 1996. The key features of the new digital sensors include a wide measurement range of between ±120 g and ±480 g and the choice of communication via the SPI or the PSI5-V1.3 interface. Peripheral sensors are located at the outermost points of a vehicle's engine compartment, at the sides, or at the rear, thus enabling them to recognize a collision quickly. However, the new fifth-generation models can do more than simply register a crash. In just a few milliseconds, they transfer to the airbag control unit all the data needed by the electronics system to determine with absolute certainty whether a collision is minor or serious. The control unit checks the plausibility of the incoming sensor data before deciding which vehicle restraint systems (e.g. front, head or side airbag and seat-belt pretensioners) to activate.

Four measurement ranges, two sensors, straightforward integration Apart from their measurement ranges, the two new sensors are of virtually identical design. The SMA58x can be switched from ±120 g to ±240 g and is designed to be integrated into the peripheral side collision sensors. The SMA59x, with twice the measurement range, is specially designed for front collisions. Both sensors measure along the Y axis. The 10-bit measuredvalue resolution and measurement range limit values are used to calculate sensitivity values of between 1 LSB/g and 4 LSB/g.

Thanks to the PSI5-V.1.3 bus interface, the sensors can be easily integrated, provided the airbag control unit also features a Peripheral Sensor Interface 5. Up to four bus users can then be operated in parallel or in series. To ensure the databus continues to function smoothly under such conditions, the new acceleration sensors feature an IDATA pin, which is used to select filters or attenuators with customer-specific dimensions. This wiring is integrated into the housing of the peripheral sensors along with the sensor chip.

Bosch engineers have equipped the SMA58x and the SMA59x with an ultra effective offset controller. This automatically makes both slow and fast offset adjustments. As a result, the sensors are very resilient to physical disturbances such as vibrations or significant fluctuations in ambient temperature. Two selectable low-pass filters with cut-off frequencies of 213 Hz and 416 Hz are also used to enhance signal conditioning.

Background information on MEMS technology Bosch has shaped the development of MEMS technology (micro-electromechanical systems) from the outset. The company has manufactured well
over two billion MEMS sensors since production began in 1993. Production volumes reach new highs year after year. In 2011 alone, around half a billion sensors rolled off the production lines in Reutlingen, making Bosch the global market leader. Its product portfolio comprises pressure sensors,
acceleration sensors, yaw-rate sensors, and inertial sensors as well as MEMS microphones and terrestrial magnetic field sensors for a variety of automotive and consumer electronics applications. More information on Bosch vehicle sensors is available at www.bosch-sensors.com.
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