Intermittent USB Recognition Issue

[grt951]

I am using the freescale USB CDC stack and virtual com port driver for the MCF51JE256 as a device only and have a intermittent issue where windows will not recognize the device. The hardware is to the USB app note (33ohm series resistors and 1.5k pull-up on D+) and the device will recognize roughly 50% of the time. It seems to also be PC dependent which is why I am looking at the hardware...any ideas?

Thanks,

Gary

EE

[Pepe_Ruiz]

Hi Gary,

Are you using an external 1.5K ohm resistor or the internal one?

If you use an external one you are not giving enough time to the MCU to enable properly the internal PLL and all the USB stack. remove the external pull-up resistor. the MCU already has an internal resistor that will be activated in SW.

try it and let us know if worked.

regards

[grt951 · Accepted solution]

Hi Pepe,

Thanks for the info...we have resolved the issue the internal VREG was not being supplied with the correct voltage via VBUS causing a inconsistent signal.

Thanks...