Voltage on MTDI to have logical 1 to drive LDO for VDD_SDIO

[rainman]

We are designing a board where the ESP32 is getting 3.3V for all power pins except for VDD3P3_CPU which we set to 2.8V.
This is needed because all external peripherals work at that voltage.

Now we want also use an SPI flash that runs at 1.8V. According to the datasheet we have to put MTDI to logical 1 to get VDD3P3_CPU producing 1.8V.

Should the logical 1 be 3.3V or 2.8V ?

To recap:
VDDP3P, VDDA, VDD3P3_RTC = 3.3V
VDD3P3_CPU = 2.8V

In order to have VDD_SDIO=1.8V what voltage should MTDI set to 2.8V or 3.3V?


Thanks

[ESP_Angus]

Sorry noone replied to your post earlier, rainman. The newly available Technical Reference Manual section 4.6 has the information you need.

To summarise: MTDI is powered from the VDD3P3_RTC power domain, so a "high" level will be relative to this power domain. As you're powering VDD3P3_RTC with 3.3V, you should also drive MTDI with 3.3V. (That said, as per the Datasheet Electrical Specifications table a high input is 0.75*VDD or higher (=2.4V @ 3.3V), so applying 2.8V to MTDI is also within specifications.)