The question of tolerance of Crystal (HFXO)

[Hsu]

Hi Sir,

According to the datasheet of 52840 (v1.1), in the ref. schematic, the requirement of 32M is +/- 40 ppm.

In section 5.4.4.2, for the frequency tolerance requirement of the long packet, it is +/- 30 ppm.

If we use +/` 40 ppm 32M crystal, is there any side effect if we sent the long packet?

Or we should use +/- 30 or +/- 20 ppm 32M crystal?

Thank you.

BRs, Han

[haakonsh]

If you do not use a +/- 30ppm crystal then you will experience packet loss, and you will not most likely not pass BT RF-PHY certs for Coded-PHY. 

You should use the most accurate crystal that fits your needs. Note that the +/- 30ppm limit includes crystal tolerance, temperature drift, and crystal aging. You need to add the effects of temperature and crystal aging over the lifetime of your device. 

For instance, a typical 32MHz crystal for consumer use can have a Frequency Tolerance of +/-20ppm, a Frequency shift by temperature of +/-20ppm, and aging of +/-5ppm per year. 

The worst-case scenario after 3 years of operation at high or low temperature is then  +/-(20ppm + 20ppm + 3 x 5ppm) = +/-55ppm.