Implementing a 1.8V Octospi PSRAM to an STM32 MCU powered by 3.3V

[Pahul_Singh]

Hello STM32 Folks,

I am currently working on a design that requires interfacing a high-density RAM (256 Mb or 512 Mb) with a microcontroller (STM32U5) via the HyperBus interface. The RAM module is powered by 1.8V, while the STM32U5 needs to be powered by 3.3V to support other peripherals.

I have not been able to find an example implementation of this type of design and would appreciate any insights on how to implement this successfully, particularly regarding voltage level translation between the 3.3V MCU and the 1.8V RAM.

Thanks,

[Sco]

If you want to use the MCU to support the peripherals in different power domains(3.3V + 1.8V), firstly you need to check if the MCU supports dedicated VDDIO power supply. For example: if there is a VDDIO2, it supports dedicated power domain, and the IOs which are belong to VDDIO power domain feature the XSPI, then you could use it in this way.

If unfortunately, this MCU doesn't supports multiple power domain of VDDIOs, then no choice but using level shift. But note that, when you plan to use level shift, you need to care about the bi-direction, frequency impacts.

[Pahul_Singh]

@Sco Thanks for the reply. 

I looked into the multiple options for bidirectional level shifters ICs with autodirectional sensing. I found the TXB0104/TXB0106 part that I think will work for me but it seems that this part can only handle 60 Mbps data rate for 1.8 V to 3.3V.

Do you think it would be better to use an auto-directional sensing level shifter or a direction-controlled level shifter for this application?