TTGO T-Display power section question

[PeteDD]

I am trying to completely understand the power section of the TTGO T-Display board. I am puzzled through by "V3V" (circled in red in the image attached (and with the link below), which appears only once in the board's schematic. The whole schematic is attached and also located here:
https://github.com/Xinyuan-LilyGO/TTGO- ... (6-26).pdf

Note that this is not "3V3" (which appears nowhere) nor "VDD3V3" which would make no sense on both sides of the FET Q6, but something else. Can anyone clarify what "V3V" is?

https://www.dropbox.com/scl/fi/qjlpba42 ... mlsfb&dl=0

THANKS!

[ESP_Sprite]

V3V also appears near the CP2104 (vio/regin/vdd pins) as well as on pullups for the LCD. Looking at the schematic, Q6 connects it to the 3.3V rail only if Vbus exists (the thing is plugged into USB) or PWR_EN is high. I think the logic is that when the device is not plugged into USB, the ESP32 can be put into deep sleep (making PWR_EN low) and Q6 will disconnect the pullup resistors as well as the CP2104 to stop it from wasting power.

[PeteDD]

@ESP_Sprite, Thank you. I'm not sure how I missed it on the USB chip, but I did... after lots of looking.
I also appreciate your explanation. Makes perfect sense.

Thanks again,
PeteDD

[ESP_Sprite]

FWIW, dependent on your PDF reader, Ctrl-F sometimes can help find where signals are used.

[djixon]

Its the standard design letting the board:
- in absence of USB power, to be powered from an external battery of larger nominated voltage (up to 8.4 V or so depending which U7 regulator is used, in that case BAT voltage goes through U7 which will regulate it to 3.3V)
- in absence of USB power, to be powered by an external exact 3.3V source which does not require further regulation, (marked as V3V on that schematic )
- to be powered by USB +5V VBus (in that case battery and possibly connected an external V3V source, both are cut from the board through SI2301 MOSFETs and those 5V from USB are bring to input of U7 regulator which will make it 3.3V on its output)

In such a configuration, as long as VBUS is presented (USB power is connected to board) state of signal PWR_EN does NOT impact configuration in any way. It wont be able to turn OFF the board as long as USB VBUS exists. It only can block transistor Q3 (which will turn off both MOSFETs) in absence of VBUS. So real meaning of that PWR_EN signal is PWR_ENABLE_IN_ABSENCE_OF_POWER_FROM_USB.