Darn autocorrect! "Enters the pub" =3D "Enters the pcb" "was pulses" =3D "esd pulses" On Feb 10, 2018 5:42 PM, "Sean Breheny" wrote: > This is a rather big topic. It is really quite important to consider how > static discharge could affect your product through any of its i/o or powe= r > inputs or even switches or other openings in the case. I usually employ a > combination of a ferrite bead, ceramic capacitor, and tvs diode on every > wire which leaves or enters the pub. Sometimes this scheme must be modifi= ed > because the signal on said wire is too high frequency or carries too much > current. But the general strategy is absorb-block-clamp. > > The capacitor helps to convert a very short high voltage pulse into a > longer duration but much smaller amplitude pulse (absorb). The ferrite be= ad > limits the current in the fast pulse so that parasitic inductance in the > ground path and in the capacitor do not develop a high voltage drop. (Blo= ck) > > Finally, the tvs diode clamps the remaining pulse to no greater than the > max rated voltage of the i/o pin. (Clamp) > > So the ferrite bead would be located nearest the outside world, and then > the cap and tvs diode would be in parallel between the signal line and gn= d > after the ferrite. > > I also like to maintain a separate ground "ring" around the perimeter of > the board which connects to the rest of the ground plane at only one poin= t. > The tvs diodes and esd-related caps connect to this ground and this groun= d > is also the only connection to chassis (not always feasible when you hav= e > RF signals) > > This ground ensures that transient high voltage drops due to fast was > pulses do not develop between locations on the main ground plane. > > In the end, all of this must be tested and any remaining vulnerabilities > corrected. > > I have designed 4 or 5 high volume (10k to 200k) industrial products usin= g > variations of this strategy with no problems passing esd tests and very f= ew > known field esd failures. > > Sean > > On Feb 10, 2018 12:44 PM, "Chuck Olson" wrote: > >> Fellows and Gals - >> >> It's static season here, had a customer complain about a PIC based >> product acting strangely - I *think* it's due to static damage. >> >> He purchased a replacement PIC, I included some small (180 ohm) series >> resistors for a couple of inputs - also a 1n4148 diode to attach, >> reversed biased, between the programming voltage pin (pin 4 on an 8 >> pin PIC) and VDD. >> >> Just wondering if there are any other tips or tricks I might suggest >> to him to help prevent static damage ? >> >> Chuck >> -- >> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> > --=20 http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .