Application report

Siddharth Sangam

Hi,

I am using Application report of

Crystal Oscillator and Crystal Selection for the CC26xx and CC13xx Family of Wireless MCUs by TI. In this report the formula for drive level is mentioned as shown in attachment below. Page 12

Freq = 2.4576MHz

ESR = 300

CL1 = 56pF

CL = 32pF

Cs = 5pF

VPP = 4.4V min 4.9V typ and 5.9V max

by referring this we are getting our power level as

min - 0.2853 mW

Typ - 04262 mW and

max - 0.7326 mW

But the drive level formula shown in App note AN2867 Page 15

Using this formula we get drive levels as

min - 0.457 mW

Typ - 0.735 mW and

max - 1.279 mW

There is difference between two formulas one is considering only load capacitance value in formula i.e. from TI appnote and

from ST is considering only single capacitance value in formula.

So, need to understand why there is difference in formulaes and what should be considered.

with regards,

Siddharth Sangam

8788110527

over 6 years ago

0 SVS over 6 years ago

TI__Genius 9705 points

Hi,

The TI app note you are referring to needs more clarification on the definition of peak-to-peak voltage and I am checking with our design team about it. Will provide an answer in couple of days.

Regards,

0 Siddharth Sangam over 6 years ago in reply to SVS

Intellectual 640 points

Yes sure

Also need to know one more thing that in case of more power dissipation a series current limiting resistor must be added as shown below.

Need to know how to find or calculate its value.

with regards,

Siddharth Sangam

0 Siddharth Sangam over 6 years ago in reply to Siddharth Sangam

Intellectual 640 points

Hello SVS,

Have you got any feedback regarding my query.

Siddharth Sangam

0 SVS over 6 years ago in reply to Siddharth Sangam

TI__Genius 9705 points

Hello,

On the equation to calculate drive level, the definition of voltage and load capacitor has to be clear.
In the app note AN2867 , Vpp is being measured on the CL1 cap, which is half as much as the voltage across crystal.
With this assumption, drive level should be 2 times the value obtained with the formula in TI app note. We will revise the app note to reflect this.

Regards,

0 Siddharth Sangam over 6 years ago in reply to SVS

Intellectual 640 points

Hi SVS,
Is this means that "TI" appnote should be updated??
and formula used in "ST" appnote is correct.

with regards,
Siddharth Sangam
8788110527 / 8624853728

0 Siddharth Sangam over 6 years ago in reply to Siddharth Sangam

Intellectual 640 points

??
I didnt get any feedback.

with regards,
Siddharth Sangam

0 SVS over 6 years ago in reply to Siddharth Sangam

TI__Genius 9705 points

Hi,

With the assumption that Vpp is measured across CL1 cap, the formula in TI document should be revised to 2 times its current definition. For the assumption made in the "ST" appnote, the formula in ST appnote is correct.

Regards,

0 Siddharth Sangam over 6 years ago in reply to SVS

Intellectual 640 points

Hi SVS,

Thanks for the reply.

But what about series resistor,how it control the power dissipation.

How to select its value.Can you provide the calculations regarding it.

regards,

Siddharth Sangam

0 SVS over 6 years ago in reply to Siddharth Sangam

TI__Genius 9705 points

Hello Siddharth,

Can you please provide information about the document you are referring to?

Regards,

0 Siddharth Sangam over 6 years ago in reply to SVS

Intellectual 640 points

I am considering same "ST" Appnote AN2867.

with regards,

Siddharth Sangam

0 SVS over 6 years ago in reply to Siddharth Sangam

TI__Genius 9705 points

Hello Siddharth,

We cannot comment on information provided in ST app note, it is best if you consult the authors of the app note. We are in the process of updating TI App note with the discussion on this thread, please stay tuned.

I will close this thread now, please feel free to start another thread if you have more questions,

Regards,

Clock & timing

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Application report