We have created a couple of different dongle-type devices using CYPD3123 / CYPD3125 where a Windows-machine communicates via USB 2.0 FS to the CCG3 via USB HID and it has worked well. However, in our latest design, the Windows machines didn't discover the USB device. Worked on different Linux devices, e.g. RPI. We tried to manually add some resistors to the D+/D- lines and then it worked on Windows.
So question is: When using the built-in USB FS device in CCG3, should there be serial resistors between the plug and IC on D+/D-? And if yes, what value?
1. It shall no need a serial resistors between the plug and IC on D+/D-.
2. If a serial resistors can resolve your issue, which is means the layout on D+ and D- trace should be take a look the impedance matching with 90 Ohm.