How to configure internal load capacitance for 32 MHz crystal on nRF54L (NCS 2.9.0)?

[Doris.chen]

Hi Nordic Team,

I’m currently working on a project using the nRF54L series, and we are using a 32 MHz external crystal oscillator based on the reference design. On our PCB, no external load capacitors were added, so we intend to rely entirely on the internal load capacitors provided by the SoC.

I came across this related DevZone thread about nRF5340, but I couldn’t find similar documentation or configuration options for nRF54L in NCS 2.9.0.

How to use internal capacitors on nrf5340? - Nordic Q&A - Nordic DevZone - Nordic DevZone

I’d like to ask:

1. How can I configure or tune the internal load capacitance value for the 32 MHz crystal on nRF54L?

2. Is there any register (like CLOCK.XO32M.LCCOMP) available for this SoC?

3. Are there Zephyr/NCS configuration options or APIs available in NCS 2.9.0 for this purpose?

 Additional Info:

Here is my current config setup:

CONFIG_ASSERT=n

CONFIG_CLOCK_CONTROL_NRF_K32SRC_XTAL=n

CONFIG_CLOCK_CONTROL_NRF_K32SRC_RC=y

We are currently using LFRC as our 32.768 kHz source and haven't made any changes to the 32 MHz HFXO setup, as it’s not clearly exposed in the SDK.

At this stage, we are running the radio_test sample from NCS for RF testing and frequency calibration. Since frequency accuracy is critical for RF performance, we would like to make sure the crystal load capacitance is correctly configured to minimize offset.

Thanks in advance for your support!

Best regards,
Doris

[Kazi Afroza Sultana]

Hello Doris,

You can configure internal and external load capacitors from board file (nrf54l_05_10_15_cpuapp_common.dtsi) of nRF54L15.

&lfxo {
load-capacitors = "internal";
load-capacitance-femtofarad = <15500>;
};

&hfxo {
load-capacitors = "internal";
load-capacitance-femtofarad = <15000>;
};

...

Thanks.

BR
Kazi