TPS65911: Crystal peripheral parameter selection

Chambin Zhang

Part Number: TPS65911

Hello,

From the TPS65911 datasheet, there are three parameters as follow picture marked, from reference design circuit of TPS65911, the load crystall oscillator value is 22pF as follow picture show.

Could you tell me why there is no Crystal series resistor and Crystal load capacitor in the reference design circuit? and why load crystall oscillator value is 22pF?

Thanks.

over 1 year ago

0 Conner Gillette over 1 year ago

TI__Genius 13880 points

This video explains the reasoning behind the different values chosen for the capacitors and series resistors (or lack thereof in this case). The value of 22pF would have been chosen as an optimal value for that specific crystal oscillator.

Kind regards,

Conner Gillette

0 Chambin Zhang over 1 year ago in reply to Conner Gillette

Prodigy 165 points

Hi Conner,

Thanks for your information.

From the vedio, I got a fomula as picture show:

From the crystal datasheet, I got the CL=12.5pF, so the 20pF< C1=C2 < 23pF when 2pF<Cstray<5pF, is the C1 and C2 value range right?

A question is if crystal temperatuer coifficient is -0.04ppm/C*C, working temperature range is 5C~40C, how to calculate the crytal frequency tolerance?

Addtional, does the C1,C2 capacitance impact crystal accuracy? what others factor will impact crystal work accuracy except crystal accuracy itself?

Thanks.

0 Conner Gillette over 1 year ago in reply to Chambin Zhang

TI__Genius 13880 points

1. That is correct.

2. Here is an good overview of variables related to crystal oscillators: https://ecsxtal.com/tuning-fork-crystal-frequency-and-parabolic-temperature-curve/

The frequency tolerance should be given in the crystal datasheet.

3. They will. However, you should see expected operating behavior at the recommended operating conditions, when the crystal tolerance of your crystal is within the limits given in the PMIC datasheet.

Kind regards,

Conner

0 Chambin Zhang over 1 year ago in reply to Conner Gillette

Prodigy 165 points

Hi Conner,

Thanks for your informaiton.

Could you tell me how to use parabolic coefficient to calculate crystal temperature characteristics?

For exaple, if this crystal use under 5~40C temperature range,

Thanks.

0 Conner Gillette over 1 year ago in reply to Chambin Zhang

TI__Genius 13880 points

I would recommend that you reach out to the crystal manufacturer for assistance with their part.

Kind regards,

Conner Gillette

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TPS65911: Crystal peripheral parameter selection