1
\$\begingroup\$

I have an FT231XS-R on a board that I am trying to use to convert from USB to UART. I am running into an issue where the device will enumerate sometimes (in which case it works perfectly) but not always. On occasion it will enumerate for a moment and then disappear but my board stays power just fine. Below are the schematics. I think my setup matches the self powered configuration as per the datasheet. I did remove the 47 pF caps per another post though I feel that may not be the cause of the issue. My current theory is the grounding of the shields on the usb connector but I am still uncertain.

5V_B comes from the USB connector. 3V3_B runs that 5V_B through a buck level shifter.

FTDI Schematic

USB Schematic

\$\endgroup\$
3
  • \$\begingroup\$ Since this is powered through the USB-C connector through the buck could you clarify how this is self powered when it appears to be bus powered? \$\endgroup\$
    – user471740
    Commented Dec 2 at 23:29
  • \$\begingroup\$ You need to tell more - that looks like bus powered to me, just with external regulators instead of internal regulators. But does the rest of the device power up from USB as well? Where is the regulator schematics? How much power or current your device consumes? Do 3.3V supply rise fast enough to keep relying on the internal chip reset? \$\endgroup\$
    – Justme
    Commented Dec 3 at 5:47
  • \$\begingroup\$ It looks like I was missing the connection to 3V3OUT. According to the datasheet it must be connected to VCC if VCC is provided 3V3. \$\endgroup\$
    – Sal
    Commented Dec 3 at 18:08

1 Answer 1

Reset to default
0
\$\begingroup\$

Read table 3.1.1 or 3.2.1, depending on the package, in the datasheet. It tells you exactly how to connect power pins.

The 3V3OUT pin cannot be not-connected - in no power supply configuration it should be just left floating.

This is a common problem with those chips. I have seen plenty of designs that miss it. Including mine at one time :)

\$\endgroup\$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.