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.
Here's the device http://www.nxp.com/documents/data_sheet/PESD2CAN.pdf
So, max 30pF at 1MHz, VR = 0V.
Take a bog standard 1N4148http://www.nxp.com/documents/data_sheet/1N4148_1N4448.pdf
Max 4pF at 1MHz, VR = 0V.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.