[sdiy] MIDI and ESD protection

Neil Johnson neil.johnson71 at gmail.com
Thu Feb 6 11:29:33 CET 2020


Hi,

> I wonder how I should go about protecting a 3.3V MIDI out circuit
> against 8kV contact ESD.

So HBM @ 8kV then?

> When I use a TVS with 5V working voltage, most of the time I still have
> 16-20V clamping voltage over the diode for 8kV contact pulses.

Have you measured this?

> With the 3.3V setup I only have a 10Ohm resistor limiting the current to
> my UART TX pin.
> with a 74hc14 as driver/buffer I can sink +/-20mA, but with 16V at 10 ohm I
> have much more to sink.

Which make of 74HC14 are you using?  Most versions of the 74HC14 I can
find online are designed to cope with HBM ESD strike at 2kV.

> I can't find anything about MIDI and ESD in the official specs or other
> sources.

The MIDI spec describes MIDI.  ESD is to some extent country-specific,
so anyone building a product needs to design their product to comply
with local regulations.

> I'm new to ESD. So do I miss something? Is the short pulse time not
> enough to fry the internal clamping diodes of a 74HC chip?

Are you designing a commercial product?  If so, get proper advice.  If
this is just a home synth-diy project I wouldn't worry about it.

Cheers,
Neil



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