nRF54L15 crystal load capacitor selection

[Webster Yang]

Dear Nordic teams : 

I would like to clarify the capacitor usage configuration:

1. If the firmware is configured to use the internal load capacitor and I also place external load capacitors on the crystal, will the MCU consider only the internal capacitors, or will it also take the external ones into account?

2. If the firmware is configured to use external capacitors, then only the external capacitors C1 and C2 need to be calculated, correct?

[Priyanka]

Hi,

1. If the firmware is configured to use the internal load capacitor and I also place external load capacitors on the crystal, will the MCU consider only the internal capacitors, or will it also take the external ones into account?

If you have configured to use the internal capacitors, then yes, only the internal capacitors will be used, however, the external capacitors are also physically present there in parallel with the internal capacitors, and hence this will affect the total capacitance. So we would recommend you to either use the internal or the external capacitors and not both together.

2. If the firmware is configured to use external capacitors, then only the external capacitors C1 and C2 need to be calculated, correct?

That's correct. Also, when using the external capacitors, you need to disable the internal capacitors.

-Priyanka