ESP32 S3 Boot start issue

[dkb1412]

Hello experts,

I am attaching the schematic of my custom hardware based on the ESP32-S3-WROOM-1-N16 module. The design follows the ESP32-S3 DevKit-C1 reference, and all required components are included. I am also attaching the power supply schematic to show that the power rails are clean and stable.

Use case:
I am using the ESP32-S3 as an I2C master, communicating with multiple I2C slave units. A NeoPixel LED is also connected for status indication.

Problem:
During the first boot after a manual power-on reset, everything works perfectly.
However, if the supply is removed for a long time (idle mode when the system is unused) and then reapplied, the ESP32-S3 fails to start correctly. The system appears stuck — the NeoPixel LED does not light up, the I2C bus is inactive, and the MCU does not execute any code.

If I press the reset button after this stuck state, the ESP32-S3 starts working immediately. This indicates the issue occurs only on the very first boot after a long idle period without power.

Hardware notes:
• All recommended decoupling capacitors are placed on the power rails, including a tantalum capacitor on the stacker board to prevent voltage drops when power is supplied through long cables (>15 cm).
• For troubleshooting, after a successful boot I removed the ESP32 PCB from the stacker and measured the I/O voltages. I observed a small millivolt-level voltage present on some lines.
• This small voltage appears to come from the RTC internal pull-ups powered by the RTC supercapacitor backup. To test this, I removed the super cap from the PCB, but the issue remained the same.

Additional observation:
Last night I unplugged the power supply. This morning, after plugging it back in, the ESP32-S3 again remained stuck during the first startup. Unplugging and re-plugging the power supply (which acts as a power-on reset) made it boot normally on the second attempt.

This seems like a strange issue, and it consistently happens only after long idle periods.
Has anyone experienced a similar problem, or is this a rare case?

[MicroController]

Has anyone experienced a similar problem, or is this a rare case?

There have been similar cases, see e.g. viewtopic.php?t=47172 or viewtopic.php?t=16141.
It seems to usually boil down to wrong RC circuits on the EN or BOOT strapping pin. When the capacitors are discharged after a 'long' time w/o power they take too long to charge when power is first applied and prevent the ESP from booting normally. After a short time on power the caps are charged to the correct voltage and a manual reset then leads to a successful boot.

[lbernstone]

https://docs.espressif.com/projects/esp ... set-timing