Changing VDD in STM32H7 from 3.3V to 1.8V on the fly for UHS-1 support for SDMMC?

Greetings everyone,

I'm thinking of a setup where a STM32H7 series chip is with

• a 1.2V regulator powers the core directly bypassing the LDO (REG1)
• another regulator whose output can be switched between 3.3V or 1.8V (default 3.3V on power up) powering the VDD (REG2)

After powering on the STM32H7, checking the SD card is present, it'll send the CMD11 to say the SD card that the data, cmd and clock line will switch to 1.8V. At the same time it'll configure the REG2 to switch output to 1.8V so that the IO lines would be 1.8V.

Would this setup work? This is so that we can find an inexpensive solution. Voltage translators like IP4855CX25 are expensive since they need PCBs with via under balls as its BGA pitch is 0.4mm.

@Community member​ as you're looking into DDR mode with SDMMC, any thoughts on this?

Thanks, Prithvi