ESP32 Forum

The Hardware Design Guidelines recommend placing bypass capacitors of 0.1uF on some of the VDD lines for the ESP32-S3 (EG 0.1 uF on VDD_SPI). Whenever I place these capacitors on my circuit, I get an invalid head of packet error when trying to flash the device over UART: And also when I try to read over UART using the serial monitor: I am not sure why this happens and have tried the solutions as suggested by the Troubleshooting section of the documentation:

• Trying another USB cable.

• Lowering the baud rate. I've tried 115200, 57600, 38400, 19200, 14400, 9600. At 115200 and 57600 I received the same invalid head of packet error. For the other baud rates I get a chip stopped responding error.

• Skipping chip autodetection. I have set my chip to ESP32-S3 using esptool.py

If it is any help, I am using a PCB that breaks out the ESP32-S3 pins to headers, then connecting these pins to a breadboard using jumper wires. It is on this breadboard where I am placing the bypass capacitors. I am also flashing my ESP32-S3 by using the ESP-Prog. I have the proper UART and JTAG pins connected and have verified proper functionality when I have not placed a bypass capacitor.

Any help would be appreciated. Thank you.

Sounds like the bypass capacitors somehow result in a dead short somehow. Can you measure the voltage over them?

The voltage I get over the capacitor is around 3.2V. This voltage stays consistent when I'm flashing and no matter what baud rate I try. I've also tried different capacitors and I get around the same voltage level.

Can you put the bypass caps closer to the ESP32, i.e. solder them to the PCB rather than use wires? Those wires can pick up noise from the environment and inject it into Vdd_sio. Additionally, they'll have a non-negligable inductance, likely negating the purpose of that decoupling cap.