Espressif Systems ESP Faq page 179

Chapter 5. Hardware related
5.3.36 Can I change the input voltage of UART0 of ESP8266 from 3.3 V to 1.8 V?
• Yes. VDDPST is the power domain for UART0, the input voltage of which can be 1.8 V theoretically.
5.3.37 Is the level of UART0 of ESP8266 determined by VDD (VCC_WIFI) or VDDPST
(VCC_CODEC_IO)?
• The digital power voltage is determined by VDDPST, so the level of UART0 of ESP8266 is determined by
VDDPST (hardware power domain).
5.3.38 What should be noted when I connect an external PSRAM to ESP32-D2WD?
• Please enable CPU frequece 240 Mhz and RTC clock 80 Mhz as follows:
– menuconfig > Serial flasher config > Flash SPI Speed (80 Mhz)
– Component config > CPU frequency (240 Mhz)
– Component
SPI-connected RAM
– Component config > ESP32 specific > SPI RAM config > Set RAM clock speed
(80 Mhz clock speed)
5.3.39 When the VDD power supply of ESP32 slowly rises from 0 V to 3.3 V, why does
the chip not start as usual?
• This problem occurs because the power-on sequence requirements are not met. To start the chip, when VDD
reaches 2.3 V, the EN voltage should not exceed 0.6 V.
• If the VDD rise time is too long, the RC circuit on the EN side of the chip will not be able to delay EN.
• You may modify the RC circuit, for example, increase the capacitance, adjust the resistance, or use the Reset
chip to control EN state.
• When the voltage provided to ESP32 is detected to be less than 2.3 V, you are recommended to pull down the
EN pin of ESP32.
• For ESP32 power-on sequence description, please refer to
5.3.40 When using the ESP32-WROOM-32D module, can I set GPIO12 for other uses?
• GPIO12 is a strapping pin that controls the startup voltage of SPI flash. The SPI flash startup voltage of the
ESP32-WROOM-32D module is 3.3 V, so GPIO12 needs to be pulled down during powering on.
• If you need to set GPIO12 for other uses, please use the command
esptool to set the voltage through VDD_SDIO as 3.3 V.
• It is possible to connect VDD_SDIO to 3.3 V in hardware directly without burning eFuse again.
• In the mass production stage, you can also download the firmware directly by modifying the default configura-
tion of ESP32_EFUSE_CONFIG to config_voltage = 3.3 V in config/esp32/utility.confgi in the flash download
tool.
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ESP32 Datasheet.
espefuse.py set_flash_voltage 3.3v
for external,
in the
Release master