LPC55xx Crystal less USB operation

[adam_smith]

Hi all,

I am making a design with a LPC55S28 MCU with USB communication on the FS USB0 interface.

I have seen that there is an application note TN00063 that refers to the possibility of not using a crystal on the FS USB0 interface.

Looking at the example project in that application note, I see that it uses a MCUXpresso SDK 2.6.2 version and makes use of a library called lib_fro_calib.

However, in the new SDK 2.11.0 versions, no example that I see makes use of that library and in the clock configurations that the USB project examples use, they all work with the internal FRO 96MHz clock version, not making use of it in any case of the crystal.

My question is, is it necessary to use the lib_fro_calib library for the current versions of the SDK if apparently all the examples that use the FS USB0 use the internal clock FRO 96MHz? In what cases is that note supposed to apply?

[ZhangJennie]

I am checking this will SDK team. I will keep you informed.

[adam_smith]

Any update about this question?

Thanks

[ZhangJennie · Accepted solution]

All LPC55s28 SDK11.0 usb demos don't use  lib_fro_calib lib. 

TN solution provides method to calibrate FRO. FRO is 1% accuracy while USB data transmission accuracy requirement is ±0.25%. Those SDK codes run well in normal room temperature. The demo code is only to show the LPC and board feature for user reference. If you need high accuracy internal clock under complex environment ( eg, temperature, pressure...), I suggest you refer the TN to develop your code.