LPC43xx schematic without USB

[priit_tanav]

I am designing my first LPC MCU based circuit board.

I am using these two schematics as a guidance:

https://www.nxp.com/downloads/en/schematics/LPCX43xx_18xx_V3_Schematic_Rev-B.pdf 

https://www.nxp.com/downloads/en/schematics/LPC-Link2-SCH.pdf 

How do the USB pins

• USB0_DP
• USB0_DM
• USB0_VBUS
• USB0_ID
• USB0_RREF
• USB1_DP
• USB1_DM
• USB0_VDDA3V3_DRIVER
• USB0_VDDA3V3
• USB0_VSSA_TERM
• USB0_VSSA_REF

have to be wired when USB functionality is not used?

Can they be:

a) left all unconnected?

b) USB0_VSSA_TERM and USB0_VSSA_REF connected to GND and others left unconnected?

c) or do I have to provide 3.3V to USB0_VDDA3V3 and USB0_VDDA3V3 with decoupling capacitors; and GND to USB0_VSSA_TERM and USB0_VSSA_REF even if USB functionality is not used?

Is there any difference relating to circuit design when comparing LPC43xx that has no USB functionality (e.g LPC431x) vs one that has (LPC433x etc), in case when USB functionality is not used? In particular, is it permissible to connect 3.3V to USB0_VDDA3V3 and USB0_VDDA3V3 for LPC431x that has no USB?

All information is welcome.

[ZhangJennie · Accepted solution]

Hi Priit Tänav 

usually, we use this way to handle unused pins:

- USBn_DP Can be left unconnected. If USB interface is not used, pin can be left unconnected
except in deep power-down mode where it must be externally pulled low. When the USB PHY is disabled, the pins are floating.
- USBn_DM Can be left unconnected. If USB interface is not used, pin can be left unconnected
except in deep power-down mode where it must be externally pulled low. When the
- USB PHY is disabled, the pins are floating.
- USB_AVSCC Tie to VSS.
- USB_VBUS Tie to VDD.
- USB_AVDDC3V3 Tie to VDD.
- USB_AVDDTX3V3 Tie to VDD.
- USB_AVSSTX3V3 Tie to VSS.
- USB_ID Can be left unconnected. If USB interface is not used, pin can be left unconnected.

Hope this helps.
Have a great day,
Jun Zhang

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[priit_tanav]

Thank You!

I will use that recommended routing configuration.

All the best!

Priit

[ZhangJennie]

You are welcome!