２４MHｚ Crystal Resonator Specifications

[soichiyamamoto]

Hi,

My customer use ２４MHｚ Crystal Resonator.

Please tell me a typ value and the Minimum value of "Peak-to-peak amplitude of oscillation", And Series resistor,Feedback resistor too.

Best Regards,

soichi

[naoumgitnik]

Dear Soichi,

1. The series resistor is unneeded - the crystal power is controlled automatically by the oscillator built into Vybrid.
2. The feedback resistor is unneeded - it is built into Vybrid itself.
3. The "Peak-to-peak amplitude of oscillation" parameters are controlled automatically by the oscillator built into Vybrid itself.

Is my understanding correct that the customer is trying to select the crystal type for Vybrid, please?

If so, there are requirements for it provided in the Vybrid Datasheet Table 76, in its "XTAL, EXTAL" section:

"The crystal must be rated for a maximum drive level of 100 μW or higher. An ESR (equivalent series resistance) of 80 Ω or less is recommended."

If any questions, feel free to discuss the specific crystal part numbers with us.

Regards, Naoum Gitnik.

[soichiyamamoto]

Dear Naoum,

Thank you for reply.

Is my understanding correct that the customer is trying to select the crystal type for Vybrid, please?

Yes.

Please let me ask additional question.

Q1)

My customer use 150Ω. Is that going to be a problem?

Q2)

In addition, is R151 of “TWR-VF65GS10_SCH.pdf” necessary?

Best Regards,

soichi

[naoumgitnik]

Dear Soichi,

A1) Any deviation from our topology / values does not guarantee the proper oscillator operation hence is not recommended.

A2) R151 is mandatory (see the Vybrid Errata document).

If any questions, feel free to discuss the specific crystal part numbers with us.

Regards, Naoum Gitnik.

[soichiyamamoto]

Dear Naoum,

Thank you for fast reply.

A1) Any deviation from our topology / values does not guarantee the proper oscillator operation hence is not recommended.

If there is concrete isuue, please tell me.

A2) R151 is mandatory (see the Vybrid Errata document).

If there is concrete start-up time, please tell me.

Best Regards,

soichi

[naoumgitnik]

Dear Soichi,

A1) It might even not oscillate at all - for all the temperature, voltage and material variations for both Vybrid and the crystal.

A2) Yes, as described in the Errata document, the start-up time might be too long without that resistor causing booting problems (such an issue has been already discussed in detail on the Community).

Regards, Naoum Gitnik.

[soichiyamamoto]

Dear Naoum,

Thank you for fast reply.

It is an additional question.

Q1)

If there is the aim of the recommendation level maximum of the ESR, please tell me.

Or is 80Ohm MAX?

Q2）

If there is a confirmation method that movement is right, please tell me.

Is it OK if I oscillate it?

Best Regards,

Soichi

[naoumgitnik]

Dear Soichi,

A1) Yes, 80-Ohm is the maximum value.

A2) It is not enough that the oscillator works on several boards- unfortunately, it does not prove its robustness, i.e. proper operation for all the temperature, voltage and material variations for both Vybrid and the crystal.

The oscillator circuit is not Vybrid or even Freescale specific; it is a classic Pierce oscillator scheme described in detail in literature and on the Internet.

Sincerely, Naoum Gitnik.

[soichiyamamoto]

Dear Naoum,

Thank you for reply.

My customer use ESR= 150Ohm,

Then what kind of Issue occurs?

Best regards,

sochi.

[naoumgitnik]

Dear Soichi,

As per the http://www.ti.com/lit/an/slaa322b/slaa322b.pdf tutorial, section "2.2 ESR Value":

"The oscillator becomes unstable and stops oscillation if the ESR becomes too high."

Regards, Naoum Gitnik.