RDAIRPABPSI5UG , Rev. 2.0
Freescale Semiconductor
9
Understanding the System
3.2 MMA6813KW - ECU Local Sensor
The ECU local sensor acceleration data is used by the airbag application to cross check the acceleration data received from the satellite
collision sensors, to confirm that a collision is really happening, and that airbags need to be deployed.
The local sensor used in the ARP is dual channel, and confirms both frontal and side impacts. In addition, the MMA68xx includes its own
safing block, which will compare the measured acceleration to configurable thresholds and set safing outputs accordingly. This function is
used in the ARP to enable the squib drivers, and therefore be an independent part of the system safing architecture - both the safing blocks
in the system basis chip and in the local sensor must enable the squib drivers before the application is able to fire the appropriate squibs.
3.3 MC33797 - Four Channel Squib Driver
Each channel consists of a high-side and a low-side switch. The ARP uses two MC33797 devices connected in cross-coupled mode, i.e.
high-side switch from one device and low-side switch from the other, connected to each squib or seat belt pre-tensioner. This ensures no
single point of failure in the squib output stage.
The MC33797 implements a comprehensive set of diagnostic features that allows the application to ensure that the squib driver stage is
operating correctly.
3.4 MMA5xxx - High G Satellite Collision Sensor
A single channel acceleration sensor operating in the range of 60 - 480g (depending on G-cell fitted), which includes a PSI5 V1.3 interface
for direct connection to the system basis chip. The device can operate in either asynchronous (point-to-point single sensor connection) or
synchronous (bus mode with multiple sensors connected to each interface) mode. The device can be used either for frontal collisions or
side impacts. For more information about PSI5, please refer to the PSI5 standard specification for airbag systems:
http://psi5.org/