Maximum External Clock supported by stm32F767.

[CJami]

I looked at both the datasheet and Oscillators design document for stm32 controllers. Both suggested the same speed for external Osciallaotrs for stm32F7 controllers that is 4-26 MHz.

BUT, in the stm32cubeMx it gives you option to select external HSE upto 50MHz, previous designer used the 50MHz as an HSE and the board is working fine.

My question here is what should be the maximum HSE that stm32F7 can support, apparently it can run on 50MHz HSE as well and stm32cubeMX also gives you this option?

Regards,
Hamza

[Tesla DeLorean]

Should be an fEXT parameter, 50 MHz being quite comman in this case as used by Ethernet.

You should select HSE_BYPASS mode so it doesn't drive the OSC_OUT pin.

[CJami]

So, stm32f7 will run using 50MHz HSE despite the fact that max input should be 26MHz?  But the thing is in bypass mode it will only run at 50MHz and it will not go via PLL. Where is this information documented?

[waclawek.jan · Accepted solution]

JW

[Tesla DeLorean]

The mode where it uses a crystal and uses an inverter is different to where is takes an external LVCMOS clock signal. The 26 MHz limit is that of the internal oscillator circuit.

The clock source then feeds the PLL. The clock is divided down to a suitable comparison frequency, so you can still hit the 200+ MHz numbers for the MCU off the HSE source.