ESP32-S3FN8 unable to upload firmware from USB or with serial

[pix3latedpic]

Hi everyone,
I need some technical support/help regarding the this issue. I have designed a custom PCB using ESP32-S3FN8 chip i am not able to upload any firmware to it neither able to get chip info using esptool. please refer to schematics below.

sch

2025-07-05_23-34.png (113.66 KiB) Viewed 188 times

ESP32-S3FN8

photo_2025-07-05_23-28-24.jpg (99.5 KiB) Viewed 188 times

this is the chip i used.

I am currently powering the pcb with 3.3v, bypassing the LDO for now from bench supply so there wont be any power issues. UART converter is connect to the serial interface of the chip and monitored the serial output. which appear to be like this

error

2025-07-05_23-43.png (5.65 KiB) Viewed 188 times

invalid header: 0xffffffff goes on for ever. when i press boot button and reset it goes to download mode too. so i guess logically chip is working but its not allowing to upload anything. even from esptool i am not able to get chip info.
please help me on guiding to solve this issue. I dont know if the chip is a legit chip or not.


FYI

C:\Windows\System32>esptool version
esptool v5.0.0
5.0.0

[Sprite]

Are you sure that indeed is an ESP32-S3FN8 and not a plain old suffix-less ESP32-S3? The latter does not have integrated flash and you also aren't using external flash, so it's no wonder you wouldn't be able to program the flash.

[pix3latedpic]

Hi,
thanks for the reply.
i am also not sure that it is an original ESP32-S3FN8 or not. I bought the chip from aliexpress and the seller mentioned it is legit, but i dont trust that. Later i connected an 4MB flash and i was able to upload the firmware with a serial print, just a simple serial print but it does not show anything on the terminal. Here is a screenshot of a reading chip and erasing after connecting an external flash.

erase

esp32s3-erase.png (12.13 KiB) Viewed 174 times

flashid

esp32s3-flashid.png (15.95 KiB) Viewed 174 times

I am uploading via USB and after the reset it shows this message.
ESP-ROM:esp32s3-20210327

it seems something still not working right? i am using arduino IDE and following are my configurations
GPIO0 and GPIO46 pulled high

esp32s3-prog.png (23.39 KiB) Viewed 174 times

please guide me on fixing the issue. if i need to make any hardware changes let me know.
Appreciate your support.

[Sprite]

i am also not sure that it is an original ESP32-S3FN8 or not. I bought the chip from aliexpress and the seller mentioned it is legit, but i dont trust that.

Decently sure it's original as I haven't seen 'fake' ESP32 chips yet, but it's a different model than you were intending to buy.

Later i connected an 4MB flash and i was able to upload the firmware with a serial print, just a simple serial print but it does not show anything on the terminal. Here is a screenshot of a reading chip and erasing after connecting an external flash.
esp32s3-erase.pngesp32s3-flashid.png
I am uploading via USB and after the reset it shows this message.
ESP-ROM:esp32s3-20210327

How exactly did you connect the flash? Also, what flash chip is it?

By the way, your schematic is... let's say, minimalistic to a fault. I see a lack of decoupling, no proper RC network on the EN pin, VDD_SPI connected straight to 3.3V, ... If you want this chip to actually work properly wrt WiFi/BT, I very strongly suggest you follow the hardware design guidelines we provide.

[pix3latedpic]

Thanks Sprite.
I have removed a flash chip from an ESP12F module and connected to ESP32S3

2025-07-08_13-47.png (93.85 KiB) Viewed 151 times

I followed the design guide for connecting it. I know there is lack of decoupling and stuff which will be fixed after testing.
later i have changed USB mode to Hardware CDC and was able to get the serial print output. But is this the right way? when i upload any sketch with wifi, like wifi scanner ... the terminal output shows its getting corrupted and stuff. So 4MB flash is not enough? (i erase the flash every time before uploading)

Code: Select all

01:17:12.572 -> Guru Meditation Error: Core  0 panic'ed (LoadProhibited). Exception was unhandled.
01:17:12.572 -> 
01:17:12.572 -> Core  0 register dump:
01:17:12.572 -> PC      : 0x420622f2  PS      : 0x00060630  A0      : 0x8205713c  A1      : 0x3fca4fc0  
01:17:12.572 -> A2      : 0x00000007  A3      : 0x00000008  A4      : 0x00000006  A5      : 0x3fcb808c  
01:17:12.572 -> A6      : 0x3fcef940  A7      : 0x0000cdcd  A8      : 0x820622ed  A9      : 0x3fca4f90  
01:17:12.572 -> A10     : 0x00000000  A11     : 0x3fcb808c  A12     : 0x00000007  A13     : 0x3fcae4c8  
01:17:12.572 -> A14     : 0x4037b414  A15     : 0x00000000  SAR     : 0x00000016  EXCCAUSE: 0x0000001c  
01:17:12.572 -> EXCVADDR: 0x0000cdc0  LBEG    : 0x40056f5c  LEND    : 0x40056f72  LCOUNT  : 0xffffffff  
01:17:12.572 -> 
01:17:12.572 -> 
01:17:12.572 -> Backtrace: 0x420622ef:0x3fca4fc0 0x42057139:0x3fca4fe0 0x42042b02:0x3fca5000 0x4037e862:0x3fca5030
01:17:12.572 -> 
01:17:12.572 -> 
01:17:12.572 -> 
01:17:12.572 -> 
01:17:12.572 -> ELF file SHA256: 92bcf370a
01:17:12.572 -> 
01:17:12.572 -> Rebooting...
01:17:12.572 -> ESP-ROM:esp32s3-20210327
01:17:12.572 -> Build:Mar 27 2021
01:17:12.572 -> rst:0xc (RTC_SW_CPU_RST),boot:0x18 (SPI_FAST_FLASH_BOOT)
01:17:12.572 -> Saved PC:0x40377031
01:17:12.572 -> SPIWP:0xee
01:17:12.572 -> mode:DIO, clock div:1
01:17:12.572 -> load:0x3fce2810,len:0x1078
01:17:12.572 -> load:0x403c8700,len:0x4
01:17:12.572 -> load:0x403c8704,len:0xaf0
01:17:12.572 -> load:0x403cb700,len:0x2e54
01:17:12.572 -> entry 0x403c889c
01:17:12.945 -> Setup done
01:17:12.945 -> scan start

[Sprite]

Impossible to say, but an error like that (especially if it happens at the exact PC every time, you could check that) tends to point at a software issue, not a hardware one. Normally, ESP-IDF detects the amount of flash and throw an error if it's less than the program needs, so I don't think the size by itself is a problem.