At 07:11 PM 5/23/2006, Spehro Pefhany wrote: > >The trouble is that according to the data sheet my 3V zeiner can go as high > >as 3.5 when in breakdown. > > > >If the PIC's VDD is at 3.3V and the input pin is at 3.5V due to the 3V > >zeiner heating...is this bad?....how bad? > > > >I can't really find anything on the data sheet and I was hoping that someone > >out there could tell me about any latch up or other issues.. (I could lower > >the zeiner to 2.7 but I'd rather not unless I have to.) > >Zeners <= 5V breakdown have a horribly soft "knee". Make sure that the voltage >is guaranteed to be a logic 1 under all conditions (worst case with low >input voltage, series resistor chosen to be okay for maximum input voltage). >See the linked typical graph (this one for the MMBZ5221BLT1 >series). http://server2.hostingplex.com/~zstoretr/zim.pdf LM-385-2.5 shunt reference? I use them in place of zeners at that voltage. TL431 also works but not as low quiescent current as LM385 or LM285. LM385 is darned cheap in large enough quantities. dwayne -- Dwayne Reid Trinity Electronics Systems Ltd Edmonton, AB, CANADA (780) 489-3199 voice (780) 487-6397 fax Celebrating 22 years of Engineering Innovation (1984 - 2006) .-. .-. .-. .-. .-. .-. .-. .-. .-. .- `-' `-' `-' `-' `-' `-' `-' `-' `-' Do NOT send unsolicited commercial email to this email address. This message neither grants consent to receive unsolicited commercial email nor is intended to solicit commercial email. -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist