Hi Friends,
We were using LS Logic family in our designs . Now when I saw Product life cycle from TI and Fairchild I decided to use HC logic family as it reached to maturity level. But faced few problems in sinking current. Can i use AC family? What is basic difference in HC and AC from design point of view?
Regards, Sonali
AC devices are much faster than HC or LS, this means that they have much higher slew rates and hence switching currents. You (may) need much better power supply bypassing than your existing LS/HC design provides. The AC family is notorious for causing all sorts of problems if adequate power supply bypassing and good (tight) PCB layout practices are not maintained.
Be very careful replacing HC/LS with AC, especially in a production item. At the very least I would review your PCB layout and bypassing for suitability. It will most likely affect your EMC requirements too.
Dave :)
This Philips selection guide tells you the technical differences but not exactly how and why you should use these families.
A good rule is: "Use the slowest family that will do the job (assuming you are not facing obselescence problems)". That way you avoid problems such as "ground bounce" due to high transient power supply currents with the faster logic families.
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