Quick heads-up for everyone who might have ordered the breakout board based on design files I uploaded to github before Dec. 28th.
As Peter Bell found out, the voltage divider that provides VDD_USB to the LEA module is not adequate, the impedance is way too high and since the current drawn by the VDD_USB pin is quite variable, there is little chance to dimension it correctly. However, it might still be possible to salvage the boards. I suggested, and Peter verified it, that replacing R7 with a red LED (0603 footprint), oriented such that the cathode connects to VDD_USB, will provide an adequate supply to the pin and might even double as an USB indicator light. I've updated the files on github on Dec. 28th and added a 3.3V LDO regulator instead of the resistor divider. This is the solution recommended in the hardware integration manual for the LEA-M8. My own boards still haven't arrived. BR, Matthias On Samstag, 26. Dezember 2020 10:06:11 CET Peter Bell wrote: > Just a quick note for anyone building these - I got my boards back and > assembled them > and everything works except for the USB port. This is being caused by the > VDD_USB > pin being fairly low-impedance and dragging down the voltage of the R7/R9 > potential > divider to about 700mV, at which point the module doesn't recognize it's > connected. > > I guess the "proper" fix would be to add another 3.3V LDO to the board that > runs from > VBUS and generates VDD_USB - but for testing purposes I removed R7 and > connected > the VDD_USB pin to the 3.3V on pin 2 of U4 - after doing this, the board > connected > and enumerated as a virtual COM port. > > Regards, > > Pete > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to > http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow > the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
