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I am looking for a 256Mbit SDRAM module in BGA format, to buy in units of 1000. However the cost for these modules are extremely high for packages using a 32bit bus in standard 3.3V voltages, however Mobile SDRAM running at 1.8V is available for the 32bit bus at half the price, or lower!

I am wondering if it is possible to 'overpower' these modules to 3.3V (probably not very likely) or get away with connecting the SDRAM without using many buffers?

I would appreciate any input.

Regards, James

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SDRAM can be a bit difficult to work with, and unless you have the tools, ability, and time to debug things then it is not a good idea to use what probably won't work. And by "tools", I mean an o-scope + probes that goes up to at least 350 MHz (1 GHz is preferred) and maybe a logic analyzer. "Ability" means that you know the SDRAM protocol inside and out. And "time" means at least several weeks to figure things out. You might also have difficulty probing the BGA pins, too.

You cannot "overpower" an SDRAM, since that'll break it. You need to convert the 3.3v signals to 1.8v, and vice versa, and you need to do it cleanly. Basically, you need buffers that will do the translation (and match the signaling specification as well). To make matters worse, some of these buffers must be bidirectional and they eat into your timing budget. If your clock rate is slow enough you might get away with this. Designing something like this requires at least an "intermediate engineer". A newbe engineer just isn't going to cut it, given all the complex timing, termination, and control that needs to be done for the buffers.

Given that, the correct 3.3v SDRAM might not be looking all that expensive after all! :) There is something to be said about using the right parts in the right places.

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  • \$\begingroup\$ Thanks for your input David. I agree about using the buffers to do the translation - I hadn't thought about the timing however. I recently have been able to reduce another area of cost substantially, so I am now able to absorb this cost of SDRAM without too much complaint! \$\endgroup\$ – James Feb 18 '12 at 17:10

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