What are Main Crystal requirements?

Singe12
Posts: 14
Joined: Mon Mar 07, 2016 10:26 am

What are Main Crystal requirements?

Postby Singe12 » Tue Nov 01, 2016 12:37 pm

Hi all,

There's several crystal types with different ESR and Load Capacitance. What you've provided to us, inside datasheet, is a Frequency range between 2 and 40 Mhz and Frequency Stability of +/-10ppm.

I want to ask:
- There's also particular requirements about ESR and Load Capacitance?
- If I choose a crystal with a frequency that isn't a multiple of 40/20/10, can I get anyway 40/80Mhz on peripherals and 160Mhz as CPU clock?

Thank you!

ESP_igrr
Posts: 950
Joined: Tue Dec 01, 2015 8:37 am

Re: What are Main Crystal requirements?

Postby ESP_igrr » Tue Nov 01, 2016 1:30 pm

I will need to check about the ESR, but for the second question, yes, you will be able to get 80/160/240 MHz CPU frequency and 80 MHz APB frequency. Crystal frequency determines CPU/APB frequency before the application startup, i.e. while first and second stage bootloaders are running. When application starts up, it enables PLL and switches the clock source to that.

ESP_igrr
Posts: 950
Joined: Tue Dec 01, 2015 8:37 am

Re: What are Main Crystal requirements?

Postby ESP_igrr » Wed Nov 02, 2016 3:44 am

Got reply from hardware guys:

Generally, once the crystal could start up to a certain amplitude, it would meet our requirements.
So don't worry about the ESR or load cap.

kostyan5
Posts: 41
Joined: Mon Mar 06, 2017 3:16 pm

Re: What are Main Crystal requirements?

Postby kostyan5 » Thu Jan 11, 2018 3:07 pm

Current data sheet and hardware design guide for ESP32 only mentions the frequency of the main crystal. Are there stability and accuracy requirements? We currently use 10ppm, but 40-50ppm are cheaper. Are those an option?

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