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Solution: Cable didn't have data lines...

I have a custom board with a CP2102N on it to go from 3.3V UART to USB via a virtual COM port. I followed the data sheet for the design, as well as referenced an Adafruit Featherboard with a similar part just as a sanity check.

My board powers up fine, the voltages appear correct, it sips 10mA of current which is the nominal calculated value it should, but when I plug the USB into my PC, I'm getting nothing...

The system is powered via 3.3V regulated from the USB port. I'm bypassing the internal regulator of the CP2102 as instructed by the datasheet. Everything I read shows that I should not need any other connections other then what is listed. I routed out DTR and RTS but they are floating unused.

Anyone see anything I missed or have any other troubleshooting ideas?

From Datasheet: enter image description here

Design: enter image description here

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2 Answers 2

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Bulk bypass capacitor C20 = 10uF may actually be too much capacitance for USB 5V supply -- try 4.7uF instead (same as the dev board). This is not well explained but is in the USB spec. Some USB hosts will have problem with 10uF or greater bulk bypass capacitance. For most applications, more bulk capacitance is better, but for USB, it needs to be 4.7uF max.

Another possible issue is the device driver. If you've never successfully operated a CP2102 on your PC, then you may need to manually install a device driver. You mentioned an Adafruit CP2102 based board, if you actually have that and it works then you can probably rule out device driver problems.

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  • \$\begingroup\$ Thanks, I have installed the driver manually, but yea I also have used boards with the same driver from Si Labs that work... My PC is a bit touchy with USB devices, I'm praying it is the capacitor! \$\endgroup\$
    – MadHatter
    Commented Jul 18, 2018 at 3:10
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Found the Issue! Was using a micro USB cable that came with a USB chargeable product I have... Turns out there are no data lines in it. Only power when I cut it open.

Different cable everything worked fine...

I didn't know they sold USB cables without data... I guess for custom applications it is cheaper? I can't believe that though.

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