KL27 - Crystal-less USB - Does it support host configuration?

[Deejay]

Hi,

For a cost sensitive solution where it requires two USB ports (1 x Host and 1 x Device), I am considering of using 2x KL27 which has the crystal-less USB feature. This way i can save the overall system cost by avoiding the external clock(s). However, as I understand from the app note AN4905, the crystal-less feature with the clock recovery circuit (to maintain the accuracy of the clocking) supports full-speed device configuration only. Can this be achieved for host (OTG) as well? If not what are the alternatives?

Thanks.

Regards,

DJ

[Jorge_Gonzalez]

Hello Devan Jeyadevan:

As stated in the appnote and in the Reference Manuals, the crystal-less feature is only for USB device mode. Moreover the KL27 only supports device mode, not host.

The closest Kinetis parts that support OTG/Host/Device are KL25/KL26. Please see the document in the next link for a general comparison:

http://cache.freescale.com/files/microcontrollers/doc/fact_sheet/LSERIESKL2FS.pdf

And the product selector guide for a more extensive comparison chart:

http://cache.freescale.com/files/microcontrollers/doc/selector_guide/KINETISLMCUSELGD.pdf

Regards!,
Jorge Gonzalez

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[Deejay]

Hi Jorge,

Thanks for your quick response with pointing out the correct device for both OTG and Device... appreciate it very much.

Now, I have another question, if I used two KL26, could I have 1 x KL26 with an external clock (8MHz) and feed its OSCCLK (8MHz) out to the 2nd KL26 CPU for its clock? Just trying to save on components.

Thanks again.

DJ

[Jorge_Gonzalez]

Hi Devan:

I understand your requirement to save costs, but I am afraid it is not possible to share the oscillator clock, especially since the USB clock must be very accurate, so best design is each MCU with its own crystal. Maybe if you do not need host and device working at the same time (in parallel), then you can use a unique USB port with only one KL26.

Regards!

Jorge Gonzalez

[Deejay]

Hi Jorge,

It's me again coming back to KL27 support for OTG. Sorry I need to make sure that i'm not overlooking the possibility of using the KL27 for OTG operation.

The KL27 datasheet (KL27P64M48SF6.pdf on page 42) says that  "The IRC48M do not meet the USB jitter specs for certification for Host mode operation".  I believe this is true only if the internal 48Mhz clock is used but it is capable of doing the OTG function with a dedicated external clock. Am I wrong? Could you please confirm on this for me?

Thanks again.

Rgds,

DJ

[Jorge_Gonzalez]

Hi Devan:

Unfortunately your assumption is incorrect. In the same note you find this:

So it does not support Host mode, not to mention OTG.

The jitter is just a general note, because some devices (e.g. MK22FN512xxx12) have the IRC48M oscillator (crystal-less device mode) and also support USB OTG or Host.

Regards!

Jorge Gonzalez

[Deejay]

Hi Jorge,

Thanks again.

Now I am looking into the MK22 series and looks like the MK22FN256VLH12 will do the job, provided this supports 2xUSB ports.

Could you please confirm this for me? Thanks.

MK22FN256VLH12​

Rgds,

DJ

[Jorge_Gonzalez]

Hi Devan:

The MK22FN256xxx12 has only 1 USB Full-Speed module, supporting OTG/Host/Device, crystal-less capable in device mode.

Regards!

Jorge Gonzalez

[Deejay]

Bummer!! :smileysad:  I guess I'm back to square one then!  The datasheets are very deceiving and misleading to some extent!

Thanks anyway Jorge and appreciate your time.

Wish you a great day!

Cheers!

DJ