[Lowfer] A timely question

[Bill Ashlock]

OK you smarties,


Here's a question about the old faithfull 555 timer IC that came up the other day when I was on the bench looking at various ways of generating a 4 min ON, 20 second OFF continuous sequence with fairly good accuracy. Due to leakage current constraints the std 555 can handle only a 3.3 meg main timing resistor and therefore one is forced into using electrolytics with  unpredictable ESRs and leakages. Then I recalled running across a CMOS version of the 555 which would make it possible to use high-value resistors along with a 10uf small-sized ceramic capacitor.

I downloaded a Fairchild spec for the 555CM and to my surprise the applicable leakage currents were not all that low. In fact there was no mention of this being a CMOS chip at all.  I did locate a spec out of a numerous others specs that definitely called out CMOS construction - and the leakage currents were very low. I am not close to my home base so I can't check to see what the designator was. Question is: What are the magic designators from various manufacturers needed to be sure the 555 I am ordering is actually CMOS?

Thanks
Bill