The DL value be considered in the design of the ECO TRIM gain?

[NXTY_Tatebayasi]

Dear supporters,

I want to use ECO（External crystal oscillator）as clock source with PSoC4.

I'm referring to the PSoC4 Archtecture TRM(Document No. 002-32818 Rev. **), but I don't understand how to handle certain parameters, so please let me know.

According to this document, Vpp, which determines the ATRIM and WDTRIM variables, can be calculated by the following formula.

I realized that DL(Drive level ; μW),ESR(ohm),CL(pF) should be substituted with the unique values that the ECO has.

On the other hand, if you refer to the ECO datasheet, the DL value may be listed as both typ and max.

Therefore, I have two questions.

1. Are ATRIM value and WDTRIM value set to safely drive within the maximum DL rating that the ECO has?

- In TRM, we are supposed to assign the maximum value of DL, but is it possible that we don't need to care about the typ and lower limit of DL value?

2. Vpp means the voltage applied to both ends of the ECO, which is controlled by the Inverting Amplifier so that it does not exceed the DL's rating? (Fig.1)

                                            Fig.1

Regards,

Chihiro Tatebayashi

[JJack · Accepted solution]

Hi Chihiro,

you can find the permissible Drive Level DL together with the ESR and recommended values of CL in the datasheet of the crystal or resonator. These three values are input data of the formula. The formula gives you the Vpp value that is necessary to obtain the specified drive level of the crystal.

A too low DL will result in low energy consumption of the oscillation but the oscillator signal is more noisy and more sensitive to noise from the outside.

When the DL is too high, then the crystal is under more mechanical stress and the power consumption of the oscillator circuit goes up. EMI radiation will rise as well.

Once the forumula has given you Vpp you can look up the settings vor ATRIM and WDTRIM in the table.

BR

JJack

[NXTY_Tatebayasi]

Hi, @JJack

I appreciated your help and thank you for elaborating on why I need to control Vpp.
So,I was able to clear my doubts.
In order to prevent the ECO from breaking down, I would first substitute the value of DLmax to get an estimation of Vpp, and then measure DL on a prototype board for the optimal solution of ATRIM and WDTRIM, and after trial and error determine the TRIM value to "achieve EMI (Vpp min)" and "not to break down the ECO (Vpp max)". 

Best Regards,

Chihiro Tatebayashi.