Payam,

My Maxim spec sheet for the MAX691A says the prop delay is 6-10nS measured at the 50% point (ie CMOS levels).

To answer question 1: You have told us what cpu you are using but not the clock rate or the type of sram. You might be using 15nS ram for all we know and a 4 Mhz 89C51. Again I revert to your original thread.

Question 2: Is it better not to use this feature? That's your decision - my decision would be to use it since it works very well. It is a precision voltage reference and a low power comparator - build your own if you wish. I have before the times of the MAX691 and it's a little tricky to get it working as reliably as the MAX691. Go the Max691 -you'll thank yourself.

Question 3: How long does a typical 3V lithium battery last? Define 'typical'?
example: CR2032 - about 3 years
SAFT LS14250 about 6-8 years
SAFT LS14500 about 10 years
Again depends on many factors - temperature, type of sram chip - some are more low power than others, how often powered on/off. These numbers were based on a memory board that used a 512k * 8 sram (low power) used in a commercial situation (25C) and powered on 24x7 most of the time. The one company serviced the machines and kept records. Your mileage may vary.

Personally, try to avoid battery backed up designs where possible - it's always a pain to change the batteries. Also it's a production hassle especially if the battery is soldered in and also if the battery is socketed, you need to ensure the battery doesn't vibrate out in service. You can't put your battery through the flow solder bath!

If this is in relation to your led signs - again I suggest using some i2C eeproms - I doubt your sign needs many changes to the messages in it's lifetime and with the endurance spec up to 10e+6 - I doubt it's a problem. Again, I suggest you copy the eeprom contents into ram for fast access.

Again, when you ask us question - please try to be specific - cpu,clock speed, part numbers. What you consider typical is not necessarily what others consider typical.