topic Re: LPC1837 USB0 in LPC Microcontrollers

LPC1837 USB0

lpcware — Wed, 15 Jun 2016 18:12:35 GMT

Content originally posted in LPCWare by vv on Mon Nov 23 09:51:47 MST 2015
Can someone double check this section of my LPC1837JET256 schematic for proper implementation of USB0? We are intending on using this interface as a USB-D MSC. We are using the Y2 12MHz XO.

When connecting this custom design to Windows 7, the computer does not enumerate and shows up in the device manager as "unknown device". USBView shows that the device is detected as a low speed device but withour proper enumeration (PID/VID is 0x00).

Using the same FW on our development kit OM13061 works fine so I believe this must be a hardware issue.

I've changed R102 & R103 to zero ohms as requested by the data sheet and still no joy.

Thoughts?

Re: LPC1837 USB0

lpcware — Wed, 15 Jun 2016 18:12:36 GMT

Content originally posted in LPCWare by bavarian on Tue Nov 24 09:24:29 MST 2015
For the community (answer to you has been given in another support forum already):

The serial resistors, the pull-downs and the capacitors on the DP and DM lines need to be removed.
For the ESD protection there are special devices on the market, also from NXP, which show up with an optimized performance in USB applications.

Regards,
NXP Support Team

Re: LPC1837 USB0

lpcware — Wed, 15 Jun 2016 18:12:36 GMT

Content originally posted in LPCWare by vv on Tue Nov 24 11:37:05 MST 2015
Just to verify:

NO 15k pull-downs, no in-series resistors, no capacitors. Simply connect DP & DM directly to the connector.

Does this also apply for USB1?

Victor

Re: LPC1837 USB0

lpcware — Wed, 15 Jun 2016 18:12:37 GMT

Content originally posted in LPCWare by vv on Tue Nov 24 12:37:04 MST 2015
SOLVED:

I swapped out the series resistors with zero ohms. Removed the 47 pF capacitors on DM & DP. Left the 15K pull-downs on board. Still no joy.

I then removed the ESD5Z3.3T1G ESD diodes on DM & DP and USB0 enumerated properly. My guess is that the USB0 is sensitive to the capacitance of the ESD diodes.

I'll consider an alternate approach for ESD protection.

Re: LPC1837 USB0

lpcware — Wed, 15 Jun 2016 18:12:38 GMT

Content originally posted in LPCWare by bavarian on Wed Nov 25 03:03:55 MST 2015
Well, you should consider this. The ESD diode you used has a huge capacitance. Somewhere in the range of 100pF @1MHz.

This is a device from NXP: http://www.nxp.com/documents/data_sheet/PRTR5V0U2X.pdf

Its capacitance is given with 1pF. Please also take care of a good placement of the device, in order to keep the parasitics low.

Regards,
NXP Support Team