Take care, there is the MAX691 and the MAX691A. Latter shows a drastically improved propagation delay time of less than 10nsec! This should be small enough for most cases.


There are several points, which affect the battery live. Two are given here:

1. Voltage at inputs of SRAM must show exactly 0V (Vcc pin and !CE input excepted, of course!), otherwise input stages are partially turned-on. But due to leakage current flowing out of inputs (driven by the 3V battery), circuitry connected to inputs will be floated, often resulting in a biasing of protection or parasitic substrate diodes. One way to circumvent this is to connect pull down resistors from these inputs to 0V. Something arround 100kOhm is approriate.
Some people will get long battery life times also without pull-down resistors. But leakage current is highly unpredictable and can drastically decrease life time of battery. So, it might be appropriate to use these pull downs in any case.

2. Very low supply current will only be observed with certain types of SRAMS. You need an LL-type, being optimized for very low data retention supply current. Just to use a standard CMOS RAM can result in a drastically increased supply current.

By the way, do you really need battery backed-up SRAM? Would instead a 28C256 also work?

Kai