Oscillators for nRF9151

[BilalMalik]

Could you please clarify for the clock and oscillator setup, are the LFXO oscillator and  LFRC RC oscillator internal oscillators on the chip? Or is an external oscillator required?

[SwRa]

HI Bilal,

The LFXO (32.768 kHz crystal oscillator) is an internal oscillator circuit that requires an external 32.768 kHz crystal to operate. The crystal itself is not integrated; you must connect it to the appropriate pins (typically XL1 and XL2) on the chip. Using the LFXO with an external crystal provides the highest clock accuracy and is recommended for applications needing precise timing.

The LFRC is a fully internal oscillator—it does not require any external components. It is always available on the chip and can be used as the low-frequency clock source.

Note:  the LFRC has a larger frequency variation compared to an external crystal (LFXO), so it is less accurate. Also, The LTE modem requires use of LFXO as the LFCLK source. Refer: https://docs.nordicsemi.com/bundle/ps_nrf9151/page/pmu_oscillators.html#ariaid-title3 

Regards,

Swathy

[BilalMalik]

Thank you Swathy for that information, it is really helpful.

Which pins should be used for XL1 and XL2 as I can't see anything on the datasheet to suggest the oscillator pinout?

[SwRa]

Hi Bilal,

SwRa said:

The LFXO (32.768 kHz crystal oscillator) is an internal oscillator circuit that requires an external 32.768 kHz crystal to operate. The crystal itself is not integrated; you must connect it to the appropriate pins (typically XL1 and XL2) on the chip. 

This is not true in case of the nRf91 series product.. Sorry for the confusion. The nRF9151(and all the other 91 devices) have both the HF and LF crystal oscillators within the package. So no external crystal is needed. 

Best Regards,

Swathy