https://devzone.nordicsemi.com/f/nordic-q-a/82014/nrf52840-usb-d-d--impedance-matchingHi 1: According to this ticket: https://devzone.nordicsemi.com/f/nordic-q-a/28335/nrf52840-usb-pins-impedance you recommend to not have any serial resistors on the D+ / D- lines. Other ref designs has 39Ohms serial resistors. 2: According toen-USTelligent Community 13Thu, 25 Nov 2021 09:39:48 GMThttps://devzone.nordicsemi.com/thread/340679?ContentTypeID=1Thu, 25 Nov 2021 09:39:48 GMT137ad170-7792-4731-bb38-c0d22fbe4515:6712e627-ba4a-4c56-adf9-6877aa04cdaaketiljo[quote user="Rulu"]What is the value of the series resistors in the bulit-in Phy?[/quote] <p>The total impedance&nbsp;will be according to the USB spec</p> [quote user="Rulu"]What would happen if there are external resistors in addition to the built-in resistors?[/quote] <p>You will most probably have problems with the signalling</p> [quote user="Rulu"]Could you explain more on how the internal circuitry synchronizes to the USB data stream (If the data is &#39;sampled&#39; in the middle of the &#39;bit periode&#39; it should be safe)?[/quote] <p>Sorry, the USB-PHY is considered a black box</p> [quote user="Rulu"]My concern is high over- / undershoot on incoming signals that may false-trigger the system causing bit errors.[/quote] <p>The best will be to hock it up to a USB tester and do an eye pattern test, like this:&nbsp;<a href="http://www.testusb.com/HSEYE.htm">http://www.testusb.com/HSEYE.htm</a></p><div style="clear:both;"></div>https://devzone.nordicsemi.com/thread/340456?ContentTypeID=1Wed, 24 Nov 2021 07:09:44 GMT137ad170-7792-4731-bb38-c0d22fbe4515:956a447a-0466-4b03-bf8b-c27937fa7decRulu<p>Thanks. Som more questions:</p> <p>What is the value of the series resistors in the bulit-in Phy?</p> <p>What would happen if there are external resistors in addition to the built-in resistors?</p> <p>Could you explain more on how the internal circuitry synchronizes to the USB data stream (If the data is &#39;sampled&#39; in the middle of the &#39;bit periode&#39; it should be safe)?</p> <p>My concern is high over- / undershoot on incoming signals that may false-trigger the system causing bit errors.</p><div style="clear:both;"></div>https://devzone.nordicsemi.com/thread/340390?ContentTypeID=1Tue, 23 Nov 2021 14:58:59 GMT137ad170-7792-4731-bb38-c0d22fbe4515:9e1b7ac5-84d2-48d1-a443-db82c04823b5ketiljo<p>The series resistors are built into the USB-PHY already. The device is designed to be used without external resistors.&nbsp;</p> <p>The speed of the USB interface isn&#39;t really a problem for the routing unless the tracks are very long. Keeping them as a matched pair is ok. For long&nbsp; tracks, stick to the USB recommended 90 ohm differential impedance.&nbsp;</p> <p>The USB isn&#39;t oversampled pr se. A faster&nbsp;48 MHz clock is needed for enough time to synchronize the clock to the data stream.</p><div style="clear:both;"></div>