HFXO _INTCAP setting

[MURAKAMI KAZUHIRO]

I want to adjust the HFXO capacitance using INTCAP.

When the XOSC32MTRIM.SLOPE (chip-specific factory calibration value) is small, the resolution of INTCAP becomes coarse, which may prevent fine adjustment. Depending on the chip, it may not be possible to achieve fine tuning, potentially causing the recommended tolerance of ±40 ppm for BLE operation to be exceeded.

Are there any countermeasures for this case?

[Havener]

Have you considered using an external capacitor in parallel with INTCAP to increase the effective tuning range and improve resolution?  puka shell necklace

[MURAKAMI KAZUHIRO]

Hi,

Is it possible to use an external capacitor together with INTCAP?

However, the specification states:

"When using external capacitors, disable the internal capacitor by setting OSCILLATORS.XOSC32M.CONFIG.INTCAP to 0."

[Ressa]

You can use external caps together with INTCAP if you want, just you need to be aware of the calculation, and make sure considering them together. 

[MURAKAMI KAZUHIRO]

Could you please explain the calculation method, configuration method, and any precautions when using them together?

[Ressa]

Hi,

Please check the HW design guideline recently released for 54L series, it has a separate chapter for HFXO and ways to calculate and set load caps:


ngl_001.pdf • Viewer • Technical Documentation


I am still not sure why you are that concerned about caps resolution, with only internal caps (and its resolution and the trim variations) you can easily stay within 40 ppm requirements. 

Best regards,
Ressa

[MURAKAMI KAZUHIRO]

Thank you for the HW design guideline.

I apologize for the confusion.

Although the settings may end up being the same, we found that—due to a calculation error in the measurement results—it can be set within 40 ppm.


best regards,