Matching circuit for nRF54L15+ nRF21540 GPIO

[Ziyao Zhou]

Hi

I remember the Devzonw could ask for hardware instructions. My matching circuir has used the nRF54L15 reference design and nRF21540 DK design, all the value is the same.

Another question would be whether I could remove the 32.768 kHz ocsillators due to limited space, what would be the effect if I remove it.

The third question would be if the I2C GPIO has its pull up resistorm would it be better to use the external pull-up resistor? Or could I use them both? Is this the same crystal using in the reference design:

Last one would be what is the relationship between NRF54L15-CAAA-R and NRF54L15-CAAA-R7

[Asbjørn]

Hello Zhou,

nRF54L15

• C2 I assume is 10uF? https://docs.nordicsemi.com/bundle/ps_nrf54L15/page/chapters/ref_circuitry.html

nRF21540

• Decoupling on VDD? We have 100nF and a 10uF on our reference. Have you followed something else? https://docs.nordicsemi.com/bundle/ps_nrf21540/page/chapters/hw_layout/reference_circuitry/doc/alt1.html

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

Source: ..\pca10156-nrf54l15-dk-0_9_1.zip\PCA10156-nRF54L15-DK 0_9_1\Production files\BOM from the HW files here: https://nsscprodmedia.blob.core.windows.net/prod/software-and-other-downloads/dev-kits/nrf54l15-dk/pca10156-nrf54l15-dk-0_9_1.zip

Can also find the HW files in the Hardware files section here: https://www.nordicsemi.com/Products/Development-hardware/nRF54L15-DK/Hardware-files?lang=en#infotabs

Reel information -R vs -R7

https://docs.nordicsemi.com/bundle/nwp_024/page/WP/nwp_024/nWP_024_reel.html

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Best regards

Asbjørn

[Ziyao Zhou]

Thank you so much for your detailed reply!