Kinetis Microcontrollers中的主题 What does it take to meet the USB timing specification with the MK22FN1M0VLH12?

What does it take to meet the USB timing specification with the MK22FN1M0VLH12?

davepfaltzgraff — Wed, 07 Oct 2015 18:46:17 GMT

I have a basic design using the MK22FN512VLH12, based on the FRDM-K22F board, and want to consider using the MK22FN1M0VLH12 as an upgrade path. However, I see that the 1M0 has the note: The MCGFLLCLK does not meet the USB jitter specifications.

How can this be handled? Does Freescale expect to release a version of the 1M0 in the near future that does?

Thanks.

Re: What does it take to meet the USB timing specification with the MK22FN1M0VLH12?

Jorge_Gonzalez — Wed, 07 Oct 2015 19:28:14 GMT

Hello David:

The note is for the MCGFLLCLK, but for USB you can of course use the PLL oscillator instead (MCGPLLCLK). The main difference is that there is no crystal-less USB device feature in the MK22FN1M0 as there is in the MK22FN512, so you need an external crystal/oscillator. If you need such feature (having internal IRC48M oscillator), then the closest device would be the MK24FN1M0.

Regards!,
Jorge Gonzalez

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Re: What does it take to meet the USB timing specification with the MK22FN1M0VLH12?

davepfaltzgraff — Wed, 07 Oct 2015 19:44:08 GMT

Hi Jorge,

A quick look tells me that the MK24FN1M0 is not available in a 64-pin LQFP package which was one of my objectives.

So, in order to meet the USB specification, I'd need to add an external crystal. As I understand it, this would preclude using PTA18 and PTA19 for any of the other functions.

I'm OK with that if that's the way to go. The first question that comes to ind is: How might that affect any power saving modes? For example, can I turn the external oscillator on/off as needed for USB communications?

Have I read this right?

Thanks