# How much power does DDR3 RAM draw when unused?

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.

• Don't forget about VTT termination power. Also they have some excel power calculators: micron.com/products/support/power-calc A quick look at their calc showed standby power was around 100mW. The calc seems to have really good info. Oct 3, 2012 at 16:16
• When you say "unused"? Do you mean that you could power down the RAM and lose the contents? Oct 3, 2012 at 16:22
• @Rocketmagnet: No. Good question. The RAM's contents must be maintained. Otherwise I'd just gate the power, and then the power overhead would be zero.
– thb
Oct 3, 2012 at 17:30
• @SomeHardwareGuy: You coult make your comment an answer. I would upvote it.
– thb
Oct 3, 2012 at 19:11
• @SomeHardwareGuy: If you answer and feel like extending your earlier, useful comment: what is VTT termnination power, please? I understand VDD/VCC, but VTT does not mean anything to me, nor do I understand what is terminated at VTT, nor does a search-engine search seem to turn up anything about VTT that relates to the present question. Aren't all the DDR's terminations transmission-gated when not in use? As far as I know, a CMOS transmission gate neither dissipates power, nor transmits power, nor even uses any control power when open and not switching.
– thb
Oct 3, 2012 at 19:21