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Crystal Load capacitors & ESR

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In the KSZ8863 datasheet, the crystal specification is given (table 9-3), page 85.

Here the ESR is specified to 40ohms with no minimum nor maximum marking. Load capacitance is specified to a max of 20pF.

My Selected quartz has an 18pF load and 40ohms - which should fit the specification.

Calculation in this App Note shows that 2 capacitors of 22pF are fine for an equivalent 18pF load.

One drawback is the power dissipated (measured) in the crystal is ~150uW (nominal for that type is 100uW).

The next drawback is the gain margin for starting oscillation. By adding an additional resistor next to the crystal, the gain or negative resistance margin is calculated to be ~2, where commonly available sources refer to ~5.

Empirical try-and-fail shows that the current of the crystal can be easily reduced by changing primarily selected capacitors (2x22pF) to e.g. 2x10pF. BY changing that capacitor there is an improvement in gain margin too.

Appropriate crystal for 2x10pF load has ESR on the level of 60...100ohms.

The question is if the generator circuitry inside the Switch device will stable operate with a higher ESR of crystal. Any idea on the max value (similar to the 20pF max of CL)?
 

Hi,
Calculation in this App Note shows that 2 capacitors of 22pF are fine for an equivalent 18pF load.
I don't see how you calculated this ... and what values you used as input.
Also I don't see why you did choose this Application note at all. It says it's for PICs. I don't say it's wrong, either.

Did you read the KSZ8863 related documents that the manufacturer provides? Especially the hardware design checklist and the related Errata document.

Klaus
 

Hi,

I don't see how you calculated this ... and what values you used as input.
Also I don't see why you did choose this Application note at all. It says it's for PICs. I don't say it's wrong, either.

Did you read the KSZ8863 related documents that the manufacturer provides? Especially the hardware design checklist and the related Errata document.

Klaus
Yes, I did read the related documents. But nothing helped.
 

Hi,

so you followed the hardware checklist ... but your design fails to operate properly?

Klaus
 

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