Stm32L4 at 80Mhz

[Michael Schnabel]

Posted on April 17, 2018 at 11:22

Hi,

I am using an Stm32L4 microcontroller in my Design, and want to be able to run it at up to 80mhz, but can't find any example on how to achieve this with an external crystal. The datasheet says the maximum frequency for an external crystal is 48Mhz, so I think I have to apply the correct prescaler for the 80mhz.

The other question is the correct Crystal for that task, can I use any or do I have to watch out for sth?

Currently I plan to use the Abracon ASFL1 with 32Mhz, would this fit?

Greetings

Michael

#crystal #stm32l4

[Pevy.Andy]

Posted on April 17, 2018 at 11:52

Use a lower frequency crystal and get the PLL to generate your 80MHz.

Andy

[AvaTar]

Posted on April 17, 2018 at 12:06

The other question is the correct Crystal for that task, can I use any or do I have to watch out for sth?

Currently I plan to use the Abracon ASFL1 with 32Mhz, would this fit?

If you want to use USB or ethernet, you are confronted with strict requirements for the respective peripheral clock (e.g. 50MHz for USB).

In this case, you would use a quartz which is an integer fraction of your frequency, i.e. 25MHz.

Otherwise, 32MHz is fine.

Select a proper clock divider and PLL multiplier, and you are fine with 80MHz.

Check the available divider/multiplier combinations for your L4, I have no experience with this part.

[henry.dick]

Posted on April 17, 2018 at 12:10

'

how to achieve this with an external crystal.'

a 80Mhz crystal is fairly uncommon. a 80Mhz oscillator is fairly common, however.

[waclawek.jan]

Posted on April 17, 2018 at 13:02

As Andy said above, using any crystal you can achieve higher frequency using PLL. Generally, it's better to use a lower-frequency crystal (8-10MHz as they are quite commonly found on the devboards), as the parasitics and similar have less impact.

Please read the RCC chapter in RM,  External clock source characteristics chapter in DS, and  AN2867.

JW