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.