i.MX6 Solo/DL XTALO pin capacitance

[nexy_sm]

Hi all,

I am not able to find input capacitance for XTALO pin. For XTALI there is a simulated value of 5pF but for XTAL) the same information is missing. Are they identical?

[igorpadykov]

Hi Nemanja

these parameters can be found in ibis model i.MX 6DualLIte and i.MX 6Solo IBIS Model File^{(REV 1.4.)}

Best regards
igor
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[nexy_sm]

Hi Igor,

I looked the IBIS model, but my knowledge in this area was literally zero until few hours ago. Still I do not see how to extract the capacitance value. The model gives Cpin for every pin but also package capacitance, and as far as I understood the answer lies in combining the two. Do you maybe have some hints?

Added later: The model for XTALI, XTALO and few other pins is NC, which somehow implies to not connected although I might be wrong. The truth is that for NC model there is no data given within the IBIS model.

Thank you,

Nemanja

[igorpadykov]

Hi Nemanja

you are right, ibis file gives capacitance for every pin and C_pkg, summer of two

is overall capacitance.

Best regards
igor

[nexy_sm]

Hi Igor,

this is rather way to wide range of values. For example:

[Package]
| variable      typ                 min                 max                 
R_pkg           0.2530623           0.0058833           0.551064            
L_pkg           3.74331nH           0.16939nH           6.95671nH           
C_pkg           7.39741pF           0.46418pF           134.527pF           
|
[Pin] signal_name        model_name      R_pin     L_pin     C_pin    
A2    PCIE_REXT                NC      0.448162  5.85114nH 1.30819pF
A3    PCIE_TXM                 NC      0.429313  5.53139nH 1.3572pF
A4    GND                      GND        NA        NA        NA       
A5    FA_ANA                   NC      0.403754  5.32197nH 1.15199pF
A6    USB_OTG_DP            usbdpdm    0.423339  5.05699nH 1.36064pF
A7    XTALI                    NC      0.351992  4.21633nH 1.18245pF

Cpkg goes as high as 134pF.

For other models (or for models because NC is maybe not a model) they provide Ccomp which is as I understood the capacitance seen from die to the pad.

So is there any more precise information about XTALI and XTALO capacitances?

[igorpadykov]

Hi Nemanja

recommended to use typical value.

>So is there any more precise information about XTALI and XTALO capacitances?

not, sorry.

Best regards
igor

[nexy_sm]

Hi Igor,

the problem is the datasheet gives typ. value for XTALI of about 5pF. Information for XTALO is rather missing. So IBIS model is of no big help here.

I wonder how other people chose load capacitors for their crystals.

[igorpadykov]

Hi Nemanja

if you are speaking about Table 22. XTALI and RTC_XTALI DC Parameters

i.MX 6Solo/6DualLite Applications Processors for Consumer Products ⁽

it shows "Simulated data". While ibis model provides data obtained from factory tests.

One can follow Table 2-7. Oscillator and clock recommendations i.MX6 System Development User’s Guide

https://www.nxp.com/docs/en/user-guide/IMX6DQ6SDLHDG.pdf

Best regards
igor