USB voltage regulator problem

[jimclay]

IN a custom design using the Kinetis K61 we have a directly connected USB interface (no ULPI), running in full-speed mode as a usb device, not host. It has protection diodes commonly used for a usb device connection on the D+ and D- lines. While testing our usb stack we connect and reconnect the cable multiple times. During this process we have managed to kill the interface on two boards in just a few days. The internal regulator seems to be shot as it only produces about a half volt from the 5V supplied. Static precautions are taken. The device descriptors are set to bus powered mode, no current requested.

Has this problem been seen before?  What can we do to fix and/or prevent this?

[CarlosCasillas · Accepted solution]

Hello Jim,

Did you add series ferrites on VBUS and GDN pins from USB port? You could refer to the USB connection of a Freescale Board (Freedom) which is also Bus powered; on this board, the GND and VBUS signals from USB port are connected to ferrites, but they have internal resistance of 330 ohm. You can review these details on Freedom´s schematic, available at the following link:

www.freescale.com/files/soft_dev_tools/hardware_tools/schematics/FRDM-KL25Z_SCH.pdf

Hope this information will be useful for you.

Best regards!

/Carlos.

[jimclay]

No, we did not have the series ferrites.  Thanks for the tip.