Set Flash Voltage

The espefuse.py set-flash-voltage command permanently sets the internal flash voltage regulator to either 1.8V, 3.3V or OFF. This means a GPIO can be high or low at reset without changing the flash voltage.

Positional arguments:

voltage - Voltage selection [‘1.8V’, ‘3.3V’, ‘OFF’].

Setting Flash Voltage (VDD_SDIO)

After reset, the default ESP32 behavior is to enable and configure the flash voltage regulator (VDD_SDIO) based on the level of the MTDI pin (GPIO12).

The default behavior on reset is:

MTDI	Internal Regulator
Low or unconnected	Enabled at 3.3V
High	Enabled at 1.8V

Consult ESP32 Technical Reference Manual chapter 4.8.1 “VDD_SDIO Power Domain” for details.

A combination of 3 eFuses (XPD_SDIO_FORCE, XPD_SDIO_REG, XPD_SDIO_TIEH) can be burned in order to override this behavior and disable VDD_SDIO regulator, or set it to a fixed voltage. These eFuses can be burned with individual burn-efuse commands, but the set-flash-voltage command makes it easier:

Disable VDD_SDIO Regulator

espefuse.py set-flash-voltage OFF

Once set:

VDD_SDIO regulator always disabled.
MTDI pin (GPIO12) is ignored.
Flash must be powered externally and voltage supplied to VDD_SDIO pin of ESP32.
eFuse XPD_SDIO_FORCE is burned.

Fixed 1.8V VDD_SDIO

espefuse.py set-flash-voltage 1.8V

Once set:

VDD_SDIO regulator always enables at 1.8V.
MTDI pin (GPIO12) is ignored.
External voltage should not be supplied to VDD_SDIO.
Efuses XPD_SDIO_FORCE and XPD_SDIO_REG are burned.

Fixed 3.3V VDD_SDIO

espefuse.py set-flash-voltage 3.3V

Once set:

VDD_SDIO regulator always enables at 3.3V.
MTDI pin (GPIO12) is ignored.
External voltage should not be supplied to VDD_SDIO.
Efuses XPD_SDIO_FORCE, XPD_SDIO_REG, XPD_SDIO_TIEH are burned.

Subsequent Changes

Once an eFuse is burned it cannot be un-burned. However, changes can be made by burning additional eFuses:

set-flash-voltage OFF can be changed to 1.8V or 3.3V
set-flash-voltage 1.8V can be changed to 3.3V