![]() ![]() Timing error Astable 2.25% tpical no max - suggesting just maybe up to 7% max based om monostable spec. Timing error monostable mode 1%/3% typical/max The LM555 datasheet suggests that the untrimmed accuracy of a '555 is "not too bad." IF the maker has chosen to make these accurate they can be so. What value of external resistors are you using?ĥ55 accuracy will be affected by the internal threshold levels in the ramp up / ramp down window comparators which in turn depend on fabrication issues. You are using values or parameters that are outside the reasonable range.This would be the case if eg they considered that the 555 IC did not produce overly accurately reproducible results between ICs - you can look at the datasheet to see if this may be so. SO the fact that it doesn't either suggests that either: There is no reason that P-S.P.I.C.E.* cannot model a 555 like timer to have a high degree of precision if the SPICE model makers wish it to. Wise men who at their end know dark is right because their words had forked no lightning still make obvious mistakes - the rest of us the more so. A circuit diagram of what you are doing is close to obligatory. ![]()
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