STM32H7 MCU with 1.8V Supply and FMC with LP-SDRAM

lufri · ‎2025-02-05

Hello,

I am currently in the design phase of a new circuit board. Roughly speaking, it's about connecting an STM32H7 (e.g. STM32H753XI) via FMC to an SDRAM and an FPGA. To save me the level conversion for the FPGA, it would be easiest to supply the ARM controller with 1.8V and use a 1.8V LP-SDRAM device (e.g. MT48H16M32LFB5-6). Unfortunately, I cannot evaluate this scenario with any evaluation board that I know of.

My question is, is there any information on how well LP-SDRAM works on a 1.8V powered STM32H7? Is there perhaps even a list of which memory is suitable?

Many thanks for your help!

SofLit · ‎2025-02-05

Hello @lufri and welcome to the community,

I don't have a direct answer to your question but it seems there is someone else did some tests. See this thread.

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lufri · ‎2025-02-05

Thanks for the answer. I didn't want to resurrect the old thread.

I see from the tests that it worked with a voltage scaling of 0. Since I would run the ARM in LDO mode, that would be okay.

However, we will run the controller at the maximum frequency of 480 MHz. But that doesn't change the fact that we set the FMC clock to 100 MHz using a peripheral PLL.

Unfortunately it is a bit critical not to be able to evaluate this beforehand, but I understand that this is a more specialized application and therefore there is no 1.8V evaluation board with external memory.

Another thing I noticed on the STM32H7xxI-Eval are the series resistors in the FMC bus. Unfortunately, I can't find any documentation on this either. Are they always necessary to adjust the impedance of the line or do they also serve to limit the current? Is there an app note on this that I am overlooking?