HSI vs. HSE crystals

[mattfox]

Posted on August 11, 2013 at 19:01

I've been looking at some board designs that I've found online, and it looks like some people include an external 8 MHz crystal in a resonator to run their clock.  I'm wondering what the benefit of using this external 8 MHz over using the internal 8 MHz crystal in the HSI.  Are there any benefits?  Thanks for the help in advance.

[jzawadzk]

Posted on August 11, 2013 at 23:34

With external crystal you will get better clock accuracy. This may be important, depending on application, for example if you want to use USB, you should use HSE as a clock source.

[Tesla DeLorean]

Posted on August 12, 2013 at 00:10

You need external crystals for CAN, ETHERNET and USB to meet specifications for those protocols, as the HSI's RC oscillator is not particularly stable or accurate.

The HSI is also impacted by voltage, temperature, and silicon variations.

[mattfox]

Posted on August 12, 2013 at 01:02

Oh, okay, thanks for the advice.  I think I'll keep my external crystal setup then because I'm using USB.