User Guide

PAMS
Technical Documentation
NME–3
Technical Information
Page 35
Issue 1 10/99
Figure 13. regular Shutdown
PowerOnX
PURX
Powerdown
Description of the Brownout circuit
The CD949 transceiver is permanently connected to the Car battery which
has a nominal level of 13.5 V. Since there are some systems in a car like
ignition or electirical motors, it happens frequently that the voltage drops
below 4V or even down to 0V, for times up to several seconds. Since it is
impossible to buffer the voltage for such a long time we implemented a
strategy called Brownout into GM8B Power control. The Basic idea behind
this strategy is that if the voltage drops, the MAD gets an interrupt, saves
the last state in the EEPROM, and shutsdown. When the Power is back
the Brownout logic indicates to the software that a Power drop has
happened, the software gets the data from the EEPROM, and resets the
Brownout logic.