USB Failure after reprogramming

[danielg14]

Hi,

We're near completion of a project using a K20 with USB. There appears to be an issue with with the USB hardware failing after repeated use. It basically will become undetectable, i.e. the reset command is never send from the computer.

We followed the component layout example provided by Freescale.

The problem seems to occur when a USB cable is connected to the USB port and we reprogram the board. Is this a known issue? Or could there be any other known potential cause of the USB port to become completely unresponsive?

This has happened on 3 - 5 boards so far.

[Hui_Ma]

Hi

First of all, sorry for the so later reply.

What kind of USB application you are using? USB device or host? And please provide the part number you are using?

We could make a dedicated test on out evaluation board.

We don't find issues with USB application when USB cable connected after Flash was re-programmed.

We prefer to add 0.1uF capacitor to VREGIN pin, which will make USB work stable.

Wish it helps.

Have a great day,
Ma Hui
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[danielg14]

We also noticed that one some reference designs there is a cap connecting the Vreg-in to GND, and on others it is not present. Our board does not have this capacitor.