> Hello!
> An ECU uses some PIC analog pins to connect to external sensors
> that return 0 .. 3.3V analog signal, like e.g. a TPS.
> 0603 10uF 6.3V capacitor in parallel to the PIC input, to smooth
> things out.
> Now I wonder if a zener is necessary too, to protect from ESD.
> OK, they won't harm. But are they really necessary in your opinion?
> PCB's are already made and space is little, more hand work is non
> desiderable etc.. so if they are really useful OK, else why add them..
> Thanks,
> Mario

What are your requirements? an engine ECU would usually be required to stil=
l operate to some degree with one sensor shorted to supply or ground. A min=
imum circuit for an analogue input would typically have an ESD cap on the i=
nput to chassis and a series resistor, I would then use a small dual diode =
to clamp to rail to handle short circuits and then an RC filter for anti-al=
iasing. In the past I have found that using the intrinsic diode to clamp an=
 input causes big offset problems on the other channels, on one design an i=
nput was accidently driven negative by a sine-wave as the offset voltage wa=
s missing - that was discovered when the other channels were plotted and th=
e negative half of the sine wave was clearly visible.
Regards
James
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