RDAIRPABPSI5UG , Rev. 2.0
14
Freescale Semiconductor, Inc.
Describing the Device Functions
5
Describing the Device Functions
The RDAIRBAGPSI5UG Airbag Reference Platform is aimed to cover all major functions of a true airbag system application.
The following section describes individual functions and available view using the GUI:
5.1 MC33789 - Airbag System Basis Chip
5.1.1
Power Supply - Boost Converter and Energy Reserve
Default setting for the boost converter is ON and will start up when VBATT exceeds a predefined limit. Initially, the boost converter will
charge a small capacitor. Default setting for the energy reserve is OFF to prevent excessive inrush current at key on. The firmware must
turn the energy reserve on through the PS_CONTROL register once VBOOST is stable. Firmware can monitor VBOOST through the
analog output pin selected through AI_CONTROL register. After the energy reserve is turned on, the large energy reserve capacitor (min
2200 µF) will be charged.
5.1.2
Power Supply - Energy Reserve Capacitor ESR Diagnostic
During ESR diagnostic, the energy reserve capacitor is slightly discharged and the firmware can calculate, based on the discharge rate,
the value of the capacitor's equivalent series resistance (ESR) - this is a measure of the condition of the capacitor.
5.1.3
Power Supply - Buck Converter
Buck converter is internally enabled when the VBOOST voltage is above the under-voltage lockout threshold. The firmware cannot disable
the Buck converter in the RDAIRBAGPSI5 application.
Table 5. Power Supply - Boost Converter and Energy Reserve
Define
Function
Config Register
Diagnosis
Comment
MC33789
Energy Reserve Supply
PS_CONTROL
AI_CONTROL
Table 6. Power Supply - Energy Reserve Capacitor ESR Diagnostic
Define
Function
Config Register
Diagnosis
Comment
MC33789
Energy Reserve
Capacitor Diagnostic
ESR_DIAG
ESR_DIAG
Table 7. Power Supply - Buck Converter
Define
Function
Config Register
Diagnosis
Comment
MC33789
Vcc5, DC Sensor and
Satellite Sensor Supply
PS_CONTROL
AI_CONTROL
