topic Re: USB0_VBUS connection for non-OTG devices? in LPC Microcontrollers

USB0_VBUS connection for non-OTG devices?

lpcware — Wed, 15 Jun 2016 18:34:11 GMT

Content originally posted in LPCWare by suckfish on Wed Sep 26 16:05:26 MST 2012
What's the easiest way to connect USB0_VBUS using the LPC43xx for a non-OTG USB device?

The user guide says that the pin is not 5v tolerant when VDDIO is not powered, but doesn't make a specific suggestion for connecting the pin.

The board is usb-powered, so under normal conditions, VDDIO will actually come up with a few milliseconds of usb being connected.

Looking a the Hitex eval board schematics, it connects USB0_VBUS directly to the usb connector (via only a ferrite bead).

Cheers,
Ralph.

Re: USB0_VBUS connection for non-OTG devices?

lpcware — Wed, 15 Jun 2016 18:34:12 GMT

Content originally posted in LPCWare by Daniel Widyanto on Fri Sep 28 01:49:02 MST 2012
Hi,

Which LPC43xx datasheet that you use ? The USB_VBUS pin is 5V tolerant, and supposed to be connected directly to USB VBUS (+5V) to check whether the VBUS is there (for USB connection / disconnection event).

The latest datasheet (http://www.nxp.com/documents/data_sheet/LPC4350_30_20_10.pdf) shows that P2_5 is 5V tolerant

Re: USB0_VBUS connection for non-OTG devices?

lpcware — Wed, 15 Jun 2016 18:34:12 GMT

Content originally posted in LPCWare by suckfish on Fri Sep 28 14:13:21 MST 2012
Thanks.

I was looking at UM10503, which says on page 507:

"The USB0_VBUS and USB1_VBUS pins are only 5 V tolerant when VDDIO is present. Therefore, special precautions are necessary when the USB0 controller is implemented as a USB-powered USB device ...."

Re: USB0_VBUS connection for non-OTG devices?

lpcware — Wed, 15 Jun 2016 18:34:13 GMT

Content originally posted in LPCWare by Daniel Widyanto on Sun Sep 30 21:48:45 MST 2012
Let me clarify this.

If your MCU VDD is available, but MCU VDDIO is not available, then you will have problem with the USB_VBUS pin (actually it's more like all of GPIO pins, coz the diode on the pin will not be turned on). That's what the sentence actually imposed.

If you tied your MCU VDD to the VDDIO, and USB_VBUS pin, the condition where the MCU VDD is available but VDDIO is not available will never happen. So, it's perfectly safe to connect all of these 3-pins to the USB Vbus without additional components.

Of course, I always recommend additional ESD diodes on each of USB pins (Vbus, D-, D+, GND) for better protection. But it's up to user to add it or not.