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STM32F103 USB FS: Series resistors vs total impedance (does it actually hurt the signal)
Sniper2 , 01-13-2026, 08:43 PM
why is there a pull up to 3v3?
Sniper2 , 01-13-2026, 08:43 PM
arent those usualy internal?
Sniper2 , 01-13-2026, 08:44 PM
the RP2040 required 22 ohm but for stm32 i am not sure due to contradicting info then again later you can use 0 ohm is needed
Shiro , 01-14-2026, 04:34 AM
Stm32f103 does not come with an internal D+ pull-up resistor. That’s why we have that 1.5k resistor on the D+ line. Also, I searched the internet and the F103 is definitely matching the USB impedance internally. Only 90 ohm diff pair is required ig. Some other designs also add choke but i think i wont need it on my design.
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