RE: Matching circuit for nRF54L15+ nRF21540 GPIO

Ziyao Zhou — Tue, 15 Apr 2025 12:04:58 GMT

Thank you so much for your detailed reply!

Asbjørn — Tue, 15 Apr 2025 07:21:16 GMT

Hello Zhou,

nRF54L15

nRF21540

Layout as far as I can see from the screen shot you sent

The layout is not something we would recommend. The component placement of the RF section is really important. We have a reference layout
Available here: https://docs.nordicsemi.com/bundle/ps_nrf54L15/page/chapters/ref_circuitry.html#ariaid-title4
With the layout you've gone for based on the picture you've attached I suspect that the signal going into the nRF21540 will not be optimum. You might also see issues with harmonic attenuation and potentially challenges with regulatory approval.
Have you manufactured this board already or is it possible to make some changes to it?

32.768kHz

Yes, you can remove the external crystal and use 32kRC as source https://docs.nordicsemi.com/bundle/ps_nrf54L15/page/clock.html
The cost is a bit more current consumption as the 32kRCOSC is a little bit more inaccurate compared to the crystal as source. That means the radio windows will be slightly longer to compensate for the different timing and hence consume a bit more current as a total.

I2C

You can use both, but not at the same time.
Please note that the internal pull resistors are too weak for 400 kHz operation, but will work for 100 kHz i2c transfers.

Crystal

Reel information -R vs -R7

docs.nordicsemi.com



Best regards

Asbjørn