[sdiy] MIDI and ESD protection

[rsdio at audiobanshee.com]

Hi Julian,

When I first skimmed your message, I wondered why you were asking. My reasoning was that the optoisolator chips used for MIDI are often used for protection against much higher voltages.

Then I realized that you specified the MIDI out! That’s clearly a different circuit without an optoisolator.

I assume that standard ESD protection for any exposed 3.3 V digital signal would be appropriate. Since this is a current loop and not really a voltage signal, you’ll need to take extra care that the ESD protection does not induce current to flow when it shouldn't.

Brian


On Feb 5, 2020, at 1:47 PM, Julian <elfenjunge at gmx.net> wrote:
> I wonder how I should go about protecting a 3.3V MIDI out circuit
> against 8kV contact ESD.
> 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.
> 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.
> I can't find anything about MIDI and ESD in the official specs or other
> sources.
> 
> 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?
> 
> Any insights are welcome!
> 
> Julian
>