I don't know why, but my last post is corrupt :\ Sorry for that - maybe Romilly can delete those two entries - thanks!
My problem: I've made up a circuit for HART-communication - almost everything works just fine, without the HART Sensitivity Test. Without noise, my device answers every request without errors. But if noise is coupled onto the loop - the communication produces errors.
My circuit is identical to the one in the datasheet and the application note. But here the problems start - the input filter of both circuits are different to each other - the AN input-filter's capacitor value is 4n7. In the datasheet it is 470p. The other components are equal to each other.
My capacitor's value is 4n7. But it seems, that the filter does not work properly.
There are errors at 29Hz, 63Hz, 125Hz, 250Hz and at the in band-frequency of 1700Hz. The HCF test number is 3.8.
Are there any known issues or does anybody have some information to solve the problem? Maybe setting the ICDREF may fix the problem? I'm using a reference voltage of 1,25V instead of 1,235V but therefore I'm using a different resistor, too. My voltage difference is 80mV as described in the datasheet.
I would be pleased if someone could help me.