nRF52832 external XL LF Clock

[lesockz]

Hello,

is it possible to use a external clock e.g. a digital output of a TXCO. As source for the LF clock. So the same clock source as used for the host uC can be used for the nRF52832.

Greets, Andi

[MartinBL]

Yes, the nRF52832 can accept an external 32.768 kHz clock feed.

The requirements are:

• Signal shall be fed into XL1 pin

• If low-swing sine: XL2 pin shall be grounded. Recommend >200 mVpp to ensure higher S/N ratio.

• If rail-to-rail: XL2 can be left open or grounded. Voltage requirement from GND to VDD_NRF.

Now you can start the LFCLK as if it was an external crystal source.

PS: For those who might wonder, external clock source for the 32 MHz clock is not supported. It used to be on the nRF51, but the clock module has been redesigned on the nRF52.

[Tmac]

We have a design with a 32MHz clock avaliable, its a digital clock rail to rail from 0-1.8V. We would like to use this signal to drive the HFXO and save the cost of the Xtal an synchronize the nRF52 to the external clock. Can you shed some light on why this should not be possible to do with the nRF52 as stated below. I should think that most xtal oscillators would work with an external clock directly or maybee we need to add some level shifting.

---

PS: For those who might wonder, external clock source for the 32 MHz clock is not supported. It used to be on the nRF51, but the clock module has been redesigned on the nRF52.

---