topic LPC546xx: USB1_REXT when USB1 is unused in LPC Microcontrollers

LPC546xx: USB1_REXT when USB1 is unused

giusloq — Fri, 10 Jun 2022 11:40:50 GMT

Should I connect USB1_REXT pin to an external resistor even when USB1 is not used on the board? What happens if UDB1_DM/USB1_DP/USB1_REXT are not connected, while USB1 VDD signals (USB1_AVDDC3V3, USB1_AVDDTX3V3, USB1_VBUS) are tied to VDD?

I found recommended connections of some unused pins in the datasheet, but USB1_REXT is not descripted.

Re: LPC546xx: USB1_REXT when USB1 is unused

VaneB — Tue, 14 Jun 2022 15:43:49 GMT

Hi @giusloq

You can leave the UBS1_REXT pin unconnected if you are not using USB1 functions. And if you have connected the USB1_VBUS, USB1_AVDDC3V3 and USB1_AVDDTX3V3 to VDD it doesn’t affect the UDB1_DM, USB1_DP and USB1_REXT.

B.R.

VaneB

Re: LPC546xx: USB1_REXT when USB1 is unused

giusloq — Tue, 14 Jun 2022 15:13:20 GMT

You can leave the UBS1_REXT pin unconnected if you are not using USB1 functions. And if you have connected the USB1_VBUS, USB1_AVDDC3V3, USB1_AVDDTX3V3 and USB1_AVSSTX3V3 to VDD it doesn’t affect the UDB1_DM, USB1_DP and USB1_REXT.

Ok, thank you for the answer. However I think you made an error with USB1_AVSSTX3V3: this pin should be tied to VSS, not VDD.