TLK105 / Crystal Oscillator Circuit

Ryuji

Guru 20090 points

Hello,

Could you please let me know the recommended current limiting resistor for the following Crystal?
http://www.kyocera-crystal.jp/eng/wp-content/uploads/2014/12/cx3225sb_e.pdf

This device level of drive is 10μW (100μW max.)
And CL is 8pF.
Thus I would like to use CL1=CL2=9pF and put the current limiting resistor.
However, I don't know how to decided this value.

Best Regards,
Ryuji Asaka

over 10 years ago

0 Ryuji over 10 years ago

Guru 20090 points

Hello,

Sorry I have additional question.

The CL of CX3225SB is 12pF. ( sorry 8pF is my misunderstanding)
In this case is the CL1=CL2=2*12pF - 7pF = 17pF?

Or
Is the CL = (CL1 * CL2)/(CL1+CL2) = 17pF , thus the CL1=CL2=33pF ( CL =16.5pF)

Best Regards,
Ryuji Asaka

0 Patrick OFarrell over 10 years ago in reply to Ryuji

TI__Mastermind 31600 points

Asaka-san,

You should use the second equation, but you should also account for stray capacitance due to parasitics. Therefore, the equation would be:
CL = ((CL1 * CL2)/(CL1+CL2)) + Cstray = 17pF

5pF is a typical value I have seen used for this stray capacitance.

Patrick

0 Rob Rodrigues over 10 years ago

TI__Mastermind 19780 points

Hello Asaka-san,

In regards to your current limiting resistor question, we do not have an easy to use equation to determine the drive level of the crystal. I will get back to you with a resolution.

Best Regards,

0 Ryuji over 10 years ago in reply to Rob Rodrigues

Guru 20090 points

Hello Rob san,

Thank you for the reply.
I'm looking forward to your checking.

Best Regards,
Ryuji Asaka

0 Rob Rodrigues over 10 years ago in reply to Ryuji

TI__Mastermind 19780 points

Asaka-san,

I apologize for the delay in answering your question on the current limiting resistor. This problem is a little more complicated. I expect to have an answer back to you in a couple of days.

Best Regards,

0 Ryuji over 10 years ago in reply to Rob Rodrigues

Guru 20090 points

Rob san,

Thank you for the reply.
I'm looking forward to your reply.

Best Regards,
Ryuji Asaka

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TLK105 / Crystal Oscillator Circuit