USB Device not recognized, LPC1347

[lpcware]

Content originally posted in LPCWare by jab on Thu Sep 13 08:08:34 MST 2012
Hi,

We have designed a custom board around the LPC1347. One of the features of this board is that if plugged in over USB and set into program mode the device pops up as a USB mass storage device so you can drag and drop your programming file.

Our board enumerates okay if the board is plugged into a USB hub but not directly into the computer. The User manual and data sheet recommended a 33 ohm resistor in series with each of the USB Data lines but this causes the device not to enumerate at all. With those resistors replaced with 0 ohm resistors it enumerates but only when plugged into a USB hub (powered or unpowered).

Has anyone else experienced this?

Julian

[lpcware]

Content originally posted in LPCWare by jab on Fri Sep 14 04:18:58 MST 2012
Hi,

Thanks for the advice. I went back and checked the power supply. My configurable voltage reg is putting out 4.7V which means the D+ line is pulled up to 3.8V.

I swapped the PSU to an external one (not using the voltage reg) and it seems to enumerate when the supply is 3.3V to the board. Guess the voltage reg isnt properly seated on the board and so it outputting the wrong voltage.

Thanks

Julian

[lpcware]

Content originally posted in LPCWare by Tsuneo on Thu Sep 13 18:58:46 MST 2012
Such a symptom is seen by these causes,
1) Transceiver supply
The power supply voltage to the USB transceiver is out of the operational range.
The on-chip USB transceiver of this chip is supplied from the VDD pin. Does the power source have enough capacity to drive USB line? Watch the VDD voltage with a digital storage scope. If you see any voltage drop of VDD at USB connection, it's the cause of your problem.

OR

2) D+ pullup
The value of D+ pull-up resistor is out of the spec. Or, the voltage source of pull-up is out of the operational range.
- Is the D+ pull-up 1.5k?
- Check the voltage of the pull-up source, like above method.

Tsuneo