I have a RAM-using application that
- would occasionally find extra RAM helpful, and
- can afford the extra hardware, but
- has a tight power budget.
Thus, I would include the extra RAM only if this extra RAM did not draw too much power when unused.
How can I calculate the power the RAM draws when unused?
I am trying to calculate this power as follows. Please tell me if and where I err.
Here is a sample datasheet for a 4-gigabit DDR3 chip: Micron's MT41K1GM4 DDR3L-RS-1600. Relevant specs:
- Burst refresh current: 215 mA.
- +45-degree-C temperature self refresh: 6.0 mA.
- VDD = VDDQ = 1.35 V.
As far as I know (though I could be wrong), the "Burst refresh current" is irrelevant to my question. If this is right, then I believe that I need a power-overhead budget of (6.0 mA)(1.35 V) = 8.1 mW to carry this chip when my device is not using it, which will be most of the time. By, unused, as @Rocketmagnet has observed, I mean that no reading or writing is going on; I do not mean that the RAM can forget its data.
If all this is right, I can afford the 8.1 mW. However, am I overlooking something important, please? I ask because I cannot afford much more power just to carry hardware that won't much be used.