Oscillator for USB in the STM32F413

[Yevpator]

Hello everybody!

I am going to work with USB on the STM32F413 . The datasheet says:

"The USB OTG full-speed controller requires a dedicated 48 MHz clock, which is generated by a PLL connected to the HSE oscillator"

I would like to ensure if it can work only with HSE or HSI will work too, in spite of what the datasheet says? I thought it could be not a full data, because when I select HSI as source for the PLL Spurce MUX in the CubeMX , it does not show me any error.

Thank you in advance!

[Uwe Bonnes · Accepted solution]

USB works with a stable HSE multiplied and divided so you get 48 MHZ as USB clock. Have a look at the reference manual. HSI is far off the needed stability and can not be used.

[Yevpator]

Thank you for the help!

Just to make it fully clear, assume I have a way to calibrate HSI, will USB work then ?

I didn't find in the DS USB clock stability requirements, maybe because it is given by USB.ORG and not ST, don't know...

[Uwe Bonnes]

Some STM32 Devices, e.g. STM32L0 and L4 have a USB clock recovery system (CRS) in harware. Maybe you can do something similar. But is it worth teh trouble? USB c;lock stability reqquirements you will find in the USB specs.

[Yevpator]

Thank you!

I am all for working with HSE with this specific case, I asked the last question in the sake of knowledge and also I was asked to consider getting rid of crystal. I see now that even if i found a solution for HSI inaccuracy over a wide temperature range, still it is required for USB. You helped me - appreciate that!