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]

Thanks for the quick feedback. So functionally it should work, but there is a risk of performance degradation, right? What kind of noise is the issue here? maybee its possible to filter the clock signal close to the nRF52 XC1 pin. If XC1 doesn't have to be driven rail to rail, and high frequency noise is the issue, we could add a simple R-C LPF close to the XC1 pin cutting off even below the 32MHz. This would attenuate the 32MHz to some degree and result in a sinewave input to the XC1 pin. It would also attenuate any high frequency noise coupled into the clock signal. Any idea if this would be feasible.