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PSoC 6 MCU

Contributor II

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?

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Moderator
Moderator

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.

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Employee

Are you using the internal LDO or BUCK as power regulator? If you are using BUCK, try to use LDO. There is a current limit when using BUCK.

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Contributor II

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.

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Moderator
Moderator

How about the result, did you find any shorts?

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Contributor II

I could not find any shorts.  I think some components were damaged.  The boards were working once but became bad after some modifications.

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