I'm looking for diodes to protect some CAN lines from ESD, and stumbled across a device produced by NXP, specifically for protecting CAN bus lines from ESD - and is advertised specifically as having ultra low capacitance.
So, am I missing a trick? What's so special about these ESD 'low capacitance' protection diodes? They have higher capacitance than everyday use diodes?
A normal diode is not a protection diode. A zener diode can have a capacitance of about 100pF, and that's still not a "protection diode" of the sort used against ESD.
My guess is: capacitance will act as a direct short to very short duration spikes.
But, too much capacitance would degrade your signal.
Hence there is a tradeoff.
Some times you add a small capacitor to deal with ESD.
I'm looking for diodes to protect some CAN lines from ESD, and stumbled across a device produced by NXP, specifically for protecting CAN bus lines from ESD - and is advertised specifically as having ultra low capacitance.
So, am I missing a trick? What's so special about these ESD 'low capacitance' protection diodes? They have higher capacitance than everyday use diodes?
Yes, you are, these diodes are TVS, ie back-to-back zener/avalanche breakdown diodes.
They are pulse rated at 230 watts, can take 5 amps....
They are big diodes in a small package, and the large diodes (ie large junction area) tend to have more
capacitance (because of the junction area), which obviously will load down a bus like CANBUS, hence
they have striven to keep the capacitance as low as possible while still taking 5A 40V spikes without damage.