On Fri, Nov 25, 2011 at 12:17 AM, Attila Kinali <att...@kinali.ch> wrote:
> On Thu, 24 Nov 2011 12:05:13 -0700 > Kevin Rosenberg <ke...@rosenberg.net> wrote: > > > Since frequency reference sine wave can exceed Vdd, you want to current > > limit the external clock. For example, an unterminated TBolt puts out > 0-7V > > Pk-Pk. Atmel, in an app note where they hook up the pins of an AVR > > to 220V mains, states the over/under voltage protection diodes should > > not carry more than 1 milliamp of current. But, you should both read > > the datasheet for the output voltage of the Efratom and measure Pk-Pk > > voltage output at the point of your PIC. > > Using the protection diodes as part of the circuit is bad design practice. > Use instead explicit shottky diodes (like BAT54S) for clamping. > I agree entirely. I had an AtoD converter that if I let the protection diodes conduct at all, would be several counts out. In this case, even a schottky diode wasn't enough! I ended up clamping to slightly less than Vdd using a schottky diode and a TL431 to provide about Vdd-0.2V. Orin. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.