[sdiy] MIDI and ESD protection

Julian elfenjunge at gmx.net
Thu Feb 6 11:39:56 CET 2020



Am 06.02.20 um 11:29 schrieb Neil Johnson:
> Hi,
>
>> I wonder how I should go about protecting a 3.3V MIDI out circuit
>> against 8kV contact ESD.
> So HBM @ 8kV then?
Nope IEC_61000-4-2 Level 4 8kV contact/15kV air discharge
>> 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?
This is from the TVS diode datasheets TLP diagrams and some spice
simulations I did.
>> 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.
yes thats tru. But a 2kV HBM strike has a peak current of 1.33A, while a
IEC 2kV strike has 7.5A and the 8kV has 30A.
So there is a difference.
See here:
https://www.onsemi.com/pub/Collateral/TND410-D.PDF
>> 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.
I wouldn't bother for SDIY as well. Never had problems in the last 10 years.
This is more in the commercial direction, but I want to understand it, too.

cheers,
Julian




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