USB 0 circuit on LPC4330/LPC4337

[lpcware]

Content originally posted in LPCWare by avr458 on Sun Oct 20 23:18:16 MST 2013
Hey all,

I'm working on a new design using USB 0 with otg/host/device functionality. I want the device to be bus powered or powered off a DC input voltage from a barrel jack. The reference boards (Xplorer) have a Ti USB power switch with ferrite isolation, is this overkill? I'm only using a single USB port and I want to be able to have the board run off USB or DC input and have it switch by itself. What is everyone doing for USB on their custom PCBs?

[lpcware]

Content originally posted in LPCWare by rocketdawg on Fri Nov 08 09:46:13 MST 2013
My iMAC cannot open the pdf.  It could be crappy iMac software.

[lpcware]

Content originally posted in LPCWare by avr458 on Thu Nov 07 21:48:44 MST 2013
Here is my schematic and design files
https://github.com/adamjvr/makodsp

I'd like some constructive feedback on the USB section.

[lpcware]

Content originally posted in LPCWare by bavarian on Fri Oct 25 04:30:27 MST 2013
Hi,

it depends on the operation if this power switch is an overkill or not. In a hot plug environment you don't what will be connected to the port, so you need to be prepared for short-circuit and overcurrent.

In general you also need to protect the pin USB0_VBUS against overvoltage in case the LPC4300 is not powered (VDDIO not present).
If you can ensure that VDDIO is always there when USB is connected, then you don't need to do anything.

A short chapter about this can be found here:  http://www.lpcware.com/content/nxpfile/an11392-guidelines-full-speed-usb-nxps-lpc-microcontrollers

If you want to do OTG, then the voltage divider will not work, you need to implement a more sophisticated protection (see attachment).

Regards,
NXP Support