I designed my own board but on some units the USB has a problem. When I enable USB through software the D+ line does not go to 3.3V when I measure without connecting USB to host. When host is connected it cannot enumerate. Across 4 bad boards the voltage varies from 0.6-3.0V. I checked VDDUSB is 3.3V. Everything else on the board works like SPI, capsense, and UART. These boards draw an extra 20mA current compared to good boards. I did x-rays on the boards and cannot find any shorts. What can be the problem?
Power off the board, try to measure the resistance between D+/D- and GND, if current path is exist, the resistance should be different with normal board.
I am using LDO. The resistance to D+ is 4Mohm on good board and around 10Mohm on bad board. I will try to find any shorts.
I could not find any shorts. I think some components were damaged. The boards were working once but became bad after some modifications.