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STM32 crystal less USB operation STM32L011?

Associate II


I'm looking for an mcu that can both do USB DFU programming and has and external crystal which there aren't many cheap available now (or would drop the external crystal requirements if I'd get convinced otherwise because I want it as stable as possible) for industrial application.

Now in STM32L011K4T6  datasheet page 13  there is a mention on crystal less USB operation, what does it mean? is there a way to somehow use USB to program this MCU without an st link?

also what should I be looking for  when checking if an stm32 supports connection of external crystal without bypass mode using 2 MCU pins like you normally expect? and how stable and reliable are the new crystal less MCUs that come out in comparison to old ones with externally connected crystals?

Pavel A.
Evangelist III

> crystal less USB operation, what does it mean?

This means that some STM32s can maintain USB device mode clock by SOF signals from the host, without external oscillator. Details are in the reference manual. This does not warrant stability and precision of the clock to other components; just that the USB device will work properly from the host POV.

By the way, for industrial applications USB is not a widely preferred interface (though may be suitable for firmware update or technician terminal interface).

is there a way to somehow use USB to program this MCU without an st link?

Yes, the CubeProgrammer can talk to the built-in bootloader of STM32 program over USB .

Or make a custom "bootloader" for in-app programming, based on DFU or other protocol. This is a frequent topic in this forum. 

ST Employee

Hi @MikeLemon ,

Besides to the answer from @Pavel A. , you find some more hints related to USB in the application note AN4879Introduction to USB hardware and PCB guidelines using STM32 MCUs.


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Associate II

Well it seems like the USB "type" of the L0 series is a bit different from the rest so my question was more towards what are the procedures to make it work on say "STM32L011K4T6" because it doesn't have that "Enable USB 2.0" option the other more "Main stream" MCU's have... 

Pavel A.
Evangelist III

+1 to what Pavel A. said above.

> STM32L011K4T6  datasheet page 13  there is a mention on crystal less USB operation

Copypaste error. I believe we've discussed exactly the same in the near past, maybe other 'L0x1 (USB is indicated by 2 or 3 as the last digit).


Well I just needed a saniti check because STM's marketing team tend to try to show their products have more than they realy do. Thanks.


You miss somethink L011 dont have USB at all. About DFU read AN2606