nvSRAM- Storage capacitor selection

[pjamu]

**broken link removed**

I've a question on selection of VCAP for nvSRAM. On What basis is a capacitor value decided for a particular nvSRAM density?
I was going through this document from cypress (see link above) and in page 2, under 'key characteristics' I came across values say, 68uF for a 4 MBit parallel nvSRAM? HOw is this 68 uF arrived, is there some formula?
I'd be happy if anyone could help me through this.

 

[crutschow]

It's likely determined empirically when they initially test the device. They look at the voltage drop on the capacitor during the shutdown AutoStore cycle and select a capacitor value that maintains sufficient voltage during this operation with adequate margin. The value given is the minimum recommended capacitor size. It can be larger if you like.

 

[pjamu]

Thanks! That was concise..