To calculate the real time of SRAM Data Retention for one Battery of 300mAh Capacity,
I would like to understand when have to take attention for "Max." value and when for "Typ." ?
As you see, the difference are fantastic:
Typ.[2] = 0.1 μA (0.0001 mA) => 342 years !!!
Max. = 3 μA (0.003 mA) => 11 years
If you are designing a space probe for a 12-year mission, or a pacemaker, or if you have a 12-year warranty when you sell an item, you would use the max value. If you are curious how long your game save will last, use the typical value to help make your predictions.
Just because one has a smaller max doesn’t always mean the typical value is also smaller. If they aren’t telling you, then you just literally don’t know and you have to use the max value unless you want to contact them or make your own measurements.
I would just assume it's the worst case. From what I understand, it's basically out your hands, because it's going to vary by each individual chip. Where I used to work, one of our main products had a 128kB SRAM (Samsung in DIP-32 package) with CR2032 backup. Part of my testing was using a meter (Fluke 179) to measure voltage drop between the coin cell and the SRAM VCC pin. Normally this would show 0.6mV, but less often it might be 0.4mV or 1.0mV. Rarely it would be one showing tens or hundreds of millivolts, we'd swap out this defective SRAM with another, problem solved. When the old board was redesigned later, it would read either 0 or 0.1mV. Never had a defective one of the more modern part that I can remember.
I guess moral of the story is maybe do lot tests, at least. If you're buying old NOS parts or recycled pulls, expect the worst. Measuring each one is an option, only way to be sure. Another thing that can go wrong might be like having a ceramic bypass capacitor fail short and discharge the battery, for example a surface mount ceramic cap near the edge of the board, where it's more likely to flex during handling (especially if you assemble them as panels, instead of individual boards).
Ben Boldt wrote: Thu Sep 11, 2025 6:20 am
If you are designing a space probe for a 12-year mission, or a pacemaker, or if you have a 12-year warranty when you sell an item, you would use the max value. If you are curious how long your game save will last, use the typical value to help make your predictions.
Just because one has a smaller max doesn’t always mean the typical value is also smaller. If they aren’t telling you, then you just literally don’t know and you have to use the max value unless you want to contact them or make your own measurements.
