# USB termination on STM32F437xx

I'm about to layout the USB connection on our boards and wondering whether the termination resistors and pull-up on D+ are necessary when using the STM32F437xx. The datasheet tells:

No external termination series resistors are required on DP (D+) and DM (D-) pins
since the matching impedance is included in the embedded driver.


Concerning the pull-up resistor on D+ it is stated:

HNP/SNP/IP inside (no need for any external resistor)


However, all development boards I checked (Olimex STM32-H407 and ST STM32F4DISCOVERY & STM32439I-EVAL) seem to include at least the termination resistors of 22Ohms. The Pull-Up on D+ is not included.

For now, I will simply place the two resistors and go with it. Still, I would like to understand the reason why one would "double-terminate" the lines.

• If in doubt, put the pads for the resistors, and then either populate with 22Ω or 0Ω depending on which way the wind is blowing at the time. – Majenko Oct 17 '14 at 14:05
• My STM32F4DISCOVERY board has 0Ω resistors for both the STM32F4 chip's USB connection and the STM32F1's connection. That's made by ST, so I'd go with no termination, since both their datasheet and their official demo board have it that way. – Majenko Oct 17 '14 at 14:16
• @Majenko thanks for checking with the real boards. I don't have them at hand and only checked the schematics. – Arne Oct 17 '14 at 14:25