Flashing esp32-c3-wroom-02

[tom_jf]

Hi
I am about to design a PCB where I would like to use the ESP32­-C3 ­WROOM­-02 Module.
I will use an external USB to serial board for flashing the ESP32-c3. Now for the connections:
TX and RX to U0TXD and U0RXD.
But the pins GPIO9 and CHIP_PU? Is it really necessary to implement a schematic like on the development board with the 2 transistors and resistors. I am limited in space on the board and therefore would like to skip those 2 transistors.
Is there a simpler way to connect the external USB-to-Serial converter for flashing the ESP32-C3-wroom-02?
Thank you and best regards
Thomas

[ESP_Sprite]

The C3 has an internal USB-to-serial converter. Simply connect GPIO18 and 19 (iirc) to an USB connector and you're good to go. (Maybe do keep a testpoint on GPIO9 to force the device back to bootloader mode if you screw up and reconfigure one of the GPIO pins, though.)

Otherwise, if you still want an external flasher: you need either the transistor circuit or buttons or something on the CHIP_PU and GPIO8, because these need to be triggered in the right order to get into download mode. You could also add either the transistors or the buttons on an external board, though.

Do keep in mind that regardless which route you go, you always need the RC network for power on reset on CHIP_PU.

[tom_jf]

Hmmm
that's a bit contradictionary to what I see on the development board.
There they use a USB to Serial converter chip on the board.
And: USB need software on the chip that handles addressing etc.
On a virgin ESP32-C3-WROOM-02 there is no USB driver I suppose.
That might be the reason why they in clude the USB to Serial chip
on the development board.
Best regards
Thomas

[ESP_Sprite]

I had a part in designing that USB-serial-JTAG converter, I can assure you there is one in your C3 As to the devboard using a 'normal' usb-serial converter: 1. we didn't get it to work immediately after tapeout, so we defaulted to an external serial converter for that, and 2, there are a few limitations to its use, so we're not sure if we want to make it the default for new general-purpose devboards just yet.

[tom_jf]

Thanks for your answer.
So when I use a 5V to 3.3V buck converter for the power, I can directly connect USB D+ and D- to the ESP pins inspite of the fact that USB is 5V?
I'll try ....
Best regards
Thomas

[ESP_Sprite]

USB actually is 3.3V on the datalines. Only the power is 5V.

[tom_jf]

Ah, thank you.