anti ESD?

[xnihilo]

Hi there.

I was wondering how i could protect my pic based circuit from ESD.
The circuit is used in lasergame system.
Does anyone here have a clue?

thanks

[Charles Linquis]

Keep lines to the crystal very short
Put a 7V Transzorb across the power
Feed the Vcc through a schottky diode - and put
2x 10uf (low ESR) and 4x .1uf on the PIC side.
Use an LF part (so that it will run at a lower voltage)
Run it at 4MHz
put 2K in series with every input along with a .1uF to GND right at the chip.
If possible, put a 330 ohm resistor in series with every output.

This formula has always worked for me.

[xnihilo]

Hello,

Thank you for your answer.

Keep lines to the crystal very short

-> No crytal used

Put a 7V Transzorb across the power

-> what is a Transzorb?

Feed the Vcc through a schottky diode - and put
2x 10uf (low ESR) and 4x .1uf on the PIC side.

-> How will it protect the pic form ESD? It will reduce the noise for sure...

Use an LF part (so that it will run at a lower voltage)

-> What is a LF? Low Freq? What for?

Run it at 4MHz

-> I need 8MHz, but again, what does it have to do with ESD protection?

put 2K in series with every input along with a .1uF to GND right at the chip.


-> Capacitors are used to filter electrical noise, right? I'm using 47UF across the power supply anode and cathode and 0.1uf for the PIC between GND and VDD

If possible, put a 330 ohm resistor in series with every output.

Most of the components are protected against ESD, aren't they?

[CocaColaKid]

> Keep lines to the crystal very short
Minimize radiated noise levels

>Put a 7V Transzorb across the power
A varistor of sorts, helps absorb power spikes exceeding 7V

>Feed the Vcc through a schottky diode - and put
>2x 10uf (low ESR) and 4x .1uf on the PIC side.
I think this is just for filtering the power supply. The 10uF take care of the lower frequency noise and the 0.1uF take care of the high frequency noise

>Use an LF part (so that it will run at a lower voltage)
Run it at 4MHz
Consumes less power and I believe generates less noise


>put 2K in series with every input along with a .1uF to GND right at the chip.
Limits the input current and filters high frequencies

>If possible, put a 330 ohm resistor in series with every output.
Prevents over-driving the outputs

I think he was just going over the entire setup that he does when be builds something. Every little bit helps that is for certain. If I made an error in my assessment please correct me as I too need to continue learning new things.

[Charles Linquis]

A Transzorb is a good, low-voltage varistor. This keeps the Vcc from ever going above 7V.

An "LF" part is one that has LF in the part number and can run at 2V (at 4MHz).
For example: Instead of using an 18F8722, use an 18LF8722. Read the last pages
of your datasheet.

If you feed the Vcc power through a Schottky (a Schottky is a low forward voltage drop diode), then negative-going disturbances on the power supply line will not affect the PIC.
The capacitor on the PIC side of the diode is not only to add filtering, but also to provide power to the device during short negative-going transients. Since the Schottky diode has a drop of approx 0.5V, if you start with a
Vcc of 5V, after going through the diode, your PIC will only get 4.5V. Using an LF part assures that it will still be running within specifications.

The R/C network on the inputs not only protect, they help prevent false triggering of inputs
by narrow spikes.
You usually can't put much resistance in series with an output, but 330 ohms does provide a fairly good compromise.

I use the techniques for military devices, and they go through some awfully tough qualifications.

[earltyso]

For what it's worth, I agree 100% with what Charles said. In college I worked on creating a HUGE ESD database for ASIC chips in a small chiphouse in Idaho. We had to of coarse qualify Military spec parts to certain MM, HBM, & CDM (Models). blah blah..

While working in the potatoe harvesting (manufacturing equipment) industry as an intern I say my design engineer (boss) place protection to all inputs on our control boards but almost never to outputs for ESD reasons. We commonly placed a resistor, zener, cap network on all our inputs for just one reason....to IDIOT proof our boards against the assembly line. We had to gaurantee that no matter if 12V or GND -12 was connected to any input or output we would not loose a board or a PIC.

What am I getting at???

The PIC have ESD BUFFERS BUILT IN THEM, that's right all pins, have some kind of buffering (double diodes for example) on the inputs to protect them from ESD events. I am not sure to what levels (ex: HBM 5000V MM 2000V ?) If someone know what JEDEC standard they pass let me know I have not looked....I guess I should now that I am getting all preachy).

Yes you can build up static on machines, hands and touching a pcb with a pic just right could burn up a port if the ESD is high enough, I would implement the 330 resistors on outputs and zeners on Vcc mentioned below if worried that much about ESD.

I did nothing but eat, drink, sleep, think ESD for about 7 months as an intern and have not worried about it all that much with PIC's since then. Probably just a bad taste in my mouth or confidence in the designers who make PIC cores.

stepping off soapbox now.

[xnihilo]

Hello,

Thank you for all this information.
I'm reading a lot of stuff on the web for 2 days already and I could not find information about the specs of the ESD protection in the PIC16F chips.
I found a good tutorial about ESD at the DIGIKEY website and I guess it will not hurt if I use a PESD5V0LB diode on the only input pin that is in contact with the outside.

My system is a lasergame equipment. there is a wired link between two devices through a single pin. I feel this pin has to be protected against ESD as user may touch the connectors.
I read about the different kinds of protection and I think if I use the bidirectional protection diode as the PESD5V0L1BA it should be fine, it is like Transil or Transzorb.
The specs of the diode are very important and I didn't find all the parameters I have to find.

I run the PIC16F690 at 5V, 8MHz (I need this frequence for PWM, TMR0,...), with a 0.1 ceramic disc capacitor attached between VSS and VDD pins and 47UF electrolytic capacitor between power supply VDD and VSS. I'm also using ground planes.
Should I be using a protection diode rated for 5V? I read that it should be higher or equal to voltage used for the device.

I don't want to rely only on the PIC internal anti-esd protection...

[Pic2008]

Using a 5V protection diode should be fine.Make sure the response time is < 1ns, ESD rating >16kV.