nRF52 LFXO External oscillator

[Adam Sillye]

We are designing a nRF52 based circuitry based on "53.2 Schematic QFAA QFN48 with DC/DC regulator setup"

In the reference diagram, there is an Optional block for the LFXO oscillator (XL1, XL2 pins). The spec also says on p. 101 "For higher LFCLK accuracy (when better than +/- 250 ppm accuracy is required), .. LFXO .. must be used".

We want to use Enhanced Shockburst 1 Mbps, later maybe BLE, but definitely no ANT. If possible, we'd like to simplify the PCB (and also the number of suppliers). Both transmitter and receiver will be nRF52.

So, question is: the "optional" X2, C11, C12s part required for ESB radio? If not, P0.00 and P0.01 are just left open like the other unused GPIOs, right?

[Øyvind Karlsen]

Hi,

The external LFCLK is entirely optional, the advantages of using it are discussed in this post, it is written about the nRF51, but the principles are the same. When unused leave the pins unconnected as you suggest.

You can also have a look at the general PCB design guidelines for nRF52.

Best regards,

Øyvind

[Adam Sillye]

Thanks, excellent info! This case we remove that part..