topic Re: VBUS Sensing in LPC Microcontrollers

VBUS Sensing

lpcware — Wed, 15 Jun 2016 16:53:04 GMT

Content originally posted in LPCWare by Muis on Tue Jan 08 06:18:42 MST 2013
Im trying to detect upon booting a LPC11U35 wether a cable is inserted, by looking at P0.3 (VBUS), but it always returns 1 (HIGH). The manual states it should return 0 (LOW) when there is no power on VBUS, so what could be the problem?

Re: VBUS Sensing

lpcware — Wed, 15 Jun 2016 16:53:05 GMT

Content originally posted in LPCWare by wmues on Wed Jan 09 01:42:18 MST 2013
A missing pulldown resistor at P0.3? Pullup enabled in IOCON registers?

Re: VBUS Sensing

lpcware — Wed, 15 Jun 2016 16:53:05 GMT

Content originally posted in LPCWare by larsen on Sat Jan 19 18:57:40 MST 2013
did you try to measure the actual voltage on that node using a voltmeter. This could give a hint.
To do this in a simple way:
Attach a loose USB cable which you have cut in two to get access to the wires to your USB slave device with your LPC11U35. The VBUS is the red wire and GND the black.
Measure the open voltage with a voltmeter. To signal low it should be <0.8V. Now try to short the wires. This makes sure that the VBUS is 0. Your LPC11U35 should now read 0 on the relevant pin. If not - something more than a missing pull-down is definitely wrong

Re: VBUS Sensing

lpcware — Wed, 15 Jun 2016 16:53:06 GMT

Content originally posted in LPCWare by Muis on Sat Jan 19 22:08:27 MST 2013
Thanks for your help, but the problem was already solved. I thought that VBUS sensing would work 'out of the box' on the LPC11U35 quickstart board, but I needed to add a resistor, after that it worked.