User`s guide

LPC3250 Developer’s Kit - User’s Guide

Page 29

4.6 USB Interface

The OTG USB interface of the LPC3250 is connected to the USB Host interface on the QVGA Base

Board. Note that the LPC3250 USB interface can only be accessed via the USB Host interface

connector, J28, on the QVGA Base Board. Connector J26 (USB OTG/Device) on the QVGA Base

Board is not connected at all.

When the LPC3250 USB interface is used as a USB Host interface the QVGA Base Board connector

(J28) is the correct one.

When the LPC3250 USB interface is used as a USB Device interface then an adapter is needed for

J28. Two alternatives exist:

 Use a USB-A (male) to USB-mini-B (female) adapter

 Use a USB-A (male) to USB-A (male) cable when connecting to for example a PC.

4.6.1 USB Interface Note

When working in USB Device mode, there have been a few reports about incorrect operation on some

(not all) boards. The problem has been traced back to R100, which is 10K on QVGA Base Board rev

1.0 and rev 1.1. By lowering R100 to 1Kohm, USB Device operation works on these boards. This has

been done on QVGA Base Board rev 1.2 so no further actions are needed on this revision of the base

board.

See the picture below for an illustration how to change R100. Either replace it (but it is not so easy to

solder R100 (0603 sized) since it is between the USB Host and Ethernet connectors) or just add a 1K

resistor on the backside (as illustrated in Figure 7).

Figure 6 – QVGA Base Board USB Connectors

USB OTG/Device

J26

NOT USED

USB Host, J28

Connects to the

USB interface of

the LPC3250

R100, 10K

Might need change to 1K.

Note, only on QVGA Base

Board rev 1.0 and rev 1.1. On

rev 1.2 this is already changed.