AN820 Datasheet, PDF (1/5 Pages) STMicroelectronics – In cars, the number of functions carried out by electronic components

AN820
APPLICATION NOTE
INPUT/OUTPUT PROTECTION
FOR AUTOMOTIVE COMPUTER
INTRODUCTION
In cars, the number of functions carried out by electronic components has greatly increased during the last
10 years.
These functions require ever more complex calculations obliging car module designers to use µC. The
sensitivity of µC input/output (linked to the high reliability required by the automotive market), forces the
computer to be efficiently protected.
PROTECTION: AGAINST WHAT?
In the car electrical network overvoltages may occur in two ways.
– Firstly on the battery supply rail which can be solved by a good load dump protection.
– Secondly by various computer inputs/outputs. In this case the energy involved is not as high as on the
supply rail side but the characteristics of the sensor and the µC port have to be taken into account
(notably when filtering is needed).
PROTECTION BY CLAMPING DEVICES
Figure 1 shows both the symbol and the electrical characteristics of a clamping device. This kind of devic-
es suppresses positive overvoltages when they exceed the breakdown voltage V_BR.
For negative voltages the suppressor clamps at 0.6V (as a rectifier diode V_F).
Figure 1. Clamping device - Symbol and characteristics
I
VF
V
VBR
May 2004
REV. 2
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