We are currently working on integrating the MM8108-MF-15457 based on the USB network adapter reference schematic provided in the datasheet. The device is being supplied with the specified operating voltages; however, we are not observing any USB activity on the D+ and D− lines. This has been verified using a logic analyzer, and the device is not detected by the host system (no enumeration observed in Device Manager or via lsusb). We would like to understand potential causes for the lack of USB enumeration. Specifically, does this device require external firmware to be programmed prior to operation, or should it function with internal firmware as provided? Additionally, are there any common design considerations or initialization requirements that may prevent the device from enumerating properly? Any guidance or recommendations would be greatly appreciated.
Hello @Forge
There isn’t any additional software required to make the module enumerate. Are you able to share any schematic snippets?
In addition to the reference schematics, take a look at our RD09 reference design (usb dongle) - Wi-Fi HaLow RD09 | USB Dongle Reference Design
Thanks for the reply. I have ordered the PCB that is inside the example schematic files as well to test to see if it is a problem with my wiring or not. However, here is a photo of the schematic.
Thanks for sharing the schematics.
Your culprit is the TVS diodes. Looks like they’re the wrong way around and would be conducting in normal operation. For protection of the data lines you want the anode at ground.
Additionally, to maintain appropriate signal integrity of the data lines, you’ll want to choose diodes with a lower junction capacitance. It looks like the ones you have chosen are >70pF. This might work for USB2.0 full speed (~12Mbps) and lower, but for USB2.0 high speed select a TVS diode with a junction capacitance under 5pF.
While I’m yapping about the data lines, make sure the impedance of the differential pair is 90 ohms (45ohm single ended).
Other than the above, the schematics look ok. Our RD09 has slightly more capacitance on the VBAT TX line (you only have 100nF, we have 10u + 100nF) but this isnt preventing your board from enumerating. It could impact your RF performance though.
Hope that helps!