Be really careful in automotive processors. I in the last decade I have done a lot of work in automotive. Even with good power filtering esd is still a big problem. Some of the processors designed for automotive have 8 check bits on a 24 bit register and mosly function without data corruption. expect to have good filtering on power and impliment good data checking and error recovery. Engine generated electrical noise can be significant. w.. > Those caps are delicate. Automotive heating and board flex from vibratio= n > can kill them. > There are special caps that are more forgiving, look on Digikey for > automotive and boardflex ratings. Also, higher voltage parts are > generally > more robust. Thicker layers. > > > On Sun, May 19, 2013 at 7:10 AM, Electron wrote= : > >> >> Thanks for the suggestion. I just had my 2nd fault, and also in this >> case >> it was the 0603 10uF 6.3V capacitor that failed short. The MPU is sane. >> >> Is it because it's a cheap chinese capacitor bought on eBay, or such a >> cap >> is intrinsically delicate and requires ESD protection even more than the >> MPU itself? >> >> Thanks a lot. >> Mario >> >> >> At 13.54 2013.05.19, Isaac Marino Bavaresco wrote: >> >First you must ensure the Zener will not interfere with your signal. >> >Zeners have capacitance and current leakage. No problem if your signal >> >is slow and of a reasonably low impedance. >> > >> >I always use some kind of protection to MCU pins that have off-board >> >connections. >> > >> >One circuit I use is comprised of a series resistor from the connector >> >pin to the Zener's cathode (Zener anode to ground, obviously) then a >> >second resistor from the Zener's cathode to the MCU pin. If I need a >> >pull-up I connect it to the Zener's cathode also. >> > >> >If the resistor's values are correctly chosen you can communicate >> >bi-directionally (e.g. I2C). >> > >> >The first resistor is to limit current into the Zener in case of an >> >accidental connection to +12V. >> >The Zener besides protecting against ESD will protect against continued >> >connection to battery voltage. >> >The second resistor will protect the MCU's internal parasitic diodes to >> >VCC in the case where the MCU is not powered and the external >> connection >> >is being supplied a voltage large enough to the point that some of the >> >Zener current is diverted to the MCU's pin and damage it. >> > >> > >> >Best regards, >> > >> >Isaac >> > >> > >> >Em 19/05/2013 08:17, Electron escreveu: >> >> Hello! >> >> >> >> An ECU uses some PIC analog pins to connect to external sensors >> >> that return 0 .. 3.3V analog signal, like e.g. a TPS. >> >> >> >> 0603 10uF 6.3V capacitor in parallel to the PIC input, to smooth >> >> things out. >> >> >> >> Now I wonder if a zener is necessary too, to protect from ESD. >> >> >> >> OK, they won't harm. But are they really necessary in your opinion? >> >> >> >> PCB's are already made and space is little, more hand work is non >> >> desiderable etc.. so if they are really useful OK, else why add >> them.. >> >> >> >> Thanks, >> >> Mario >> >> >> > >> >-- >> >http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive >> >View/change your membership options at >> >http://mailman.mit.edu/mailman/listinfo/piclist >> >> -- >> http://www.piclist.com/techref/piclist PIC/SX FAQ & list archive >> View/change your membership options at >> http://mailman.mit.edu/mailman/listinfo/piclist >> > -- > 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 .