Hello,
I`m creating pcb with basic mcu on ATMEGA328P (Arduino UNO).
For ESD protection ISP, I2C, RST lines i have using series resistor.
I have a choice between 100, 330 and 1k.
Tell me, which face value should I choose for these purposes?
Thank you!
post a schematic of what you mean.
(since what you are saying isnot common oractice which suggests no electronic experience and you
you are just making this stuff up as you go along.
If you have a problem, explain it, but don't ask us
what is the standard vaue component to use to do something that is not standard practice.
Let's face it, if it was a stardard practice you
could just Google it but you probably already
tried that and came up empty.
State exactly what yourconcern is andehy you sre even talking about this. Instead of asking this
why don't you back up and just ask:
" Hey, should I be concerned about _____ ?"
"How should I address that ?"
(FYI, "series resistors is the wrong answer)
We can't answer your question because we
don't know what you are protecting from .
Where's the danger ? (sorce of ESD)
Look at the Atmel ATMega328 datasheet.
The RST pin has internal protection diodes.
100 in series will work pretty well. You're trying to limit the input current to 1mA to either 5V or The, while limiting the output current to 20, 25mA.
5V/100 ohms =0.050A (50mA)
The assumption is that High outputs will not be connected directly to Gnd, and Low outputs to +5V. That would lead to high currents. Also, it has been suggested the outputs have an internal resistance of around 40 ohm, further limiting current to about 35 ma. Easy enough to confirm with a resistor and multimeter.
CrossRoads:
100 in series will work pretty well. You're trying to limit the input current to 1mA to either 5V or The, while limiting the output current to 20, 25mA.
What has this to do with ESD protection?
It is clearly another XY problem.
Taken dirctly from the Bussman Technical Note 4067: http://www.cooperindustries.com/content/dam/public/bussmann/Electronics/Resources/technical-literature/Circuit%20Protection/elx-an-4067-esd-app-note.pdf. “What is ESD? Electrostatic discharge (ESD) is a growing problem within the electronic industry due to the sensitivity of high speed circuits and the growth in hand held portable products. The portable products used in everyday life have many input/output ports that connect to different devices. Human interaction with portable equipment ports is the cause of many ESD failures. Eaton offers a variety of ESD protection products that prevent damage to internal components in electronic equipment. Ideally for the best protection, these devices should be placed on the printed circuit board near the input/output ports to shunt ESD energy at the point of entry”
Get a grounding bracelet. TVS diodes are designed for protecting electronic circuits against ESD pulses. Silicon-avalanche diodes are well suited for ESD protection, with high impedance at stand-off voltage and low impedance at breakdown voltage. TVS Diodes are made with parallel opposing silicon avalanche diodes. Before you go much further read this link, Bushman published AN4067 ESD Protection for portable electronic products A series resistor would protect you some form ESD but would also protect the circuit if I/O were connected to the wrong place especially of the TVS diodes were between the resistor and the outside the board.. You need to look at the input protection circuit of the micro and see what its maximum rating is. Please know that if you exceed that you have damaged the part, it will fail, it man be right away it may be years.
Good Luck & Have Fun!
Gil
gilshultz:
A series resistor would protect you some form ESD
Let's see. ESD voltages ... lowest mentioned is 8 kV.
Let me take 1 kV for a moment. 1k resistor. Would limit discharge current to 1 kA.
Fair enough?
:o
Try this:
Let me take 1 kV for a moment. 1k resistor (rated for 1 kV). Would limit discharge current to 1 A.
OK?
Paul__B:
Let's see. ESD voltages ... lowest mentioned is 8 kV.Let me take 1 kV for a moment. 1k resistor. Would limit discharge current to 1 kA.
Fair enough?
Arduino (and nearly all other ICs) include ESD protection.The resistor may provide considerable protection depending on the ESD source. Look at HBM, CDM and MM ESD models. For CDM and MM there is no "current limiting" resistor - here even a small series resistor "eats" considerable amount of the ESD energy. Since no data is provided for the protection diodes it is hard to tell - but it needs much better analysis than simple Ohm's law application.
Let me take 1 kV for a moment. 1k resistor. Would limit discharge current to 1 kA.
1000V / 1000 Ohms makes, according to my rusty, old, not very mathematical brain, 1A. Not 1000A.
Err, yeah!
Must have been late at night.
(Looks at time posted.) It was! 
Mind you, 1 A through an ESD diode is significant.
Must have been late at night.
If you look thorough my posts you won't have to look far to find equally daft mistakes 
