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 behaviour is to enable and configure the flash voltage regulator (VDD_SDIO) based on the level of the MTDI pin (GPIO12).
The default behaviour 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 behaviour 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_FORCEis 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_FORCEandXPD_SDIO_REGare 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_TIEHare 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 OFFcan be changed to1.8Vor3.3Vset_flash_voltage 1.8Vcan be changed to3.3V