nRF52 on custom board can receive BLE packets, but not send

RE: nRF52 on custom board can receive BLE packets, but not send

SenseJo — Fri, 08 Mar 2024 13:39:35 GMT

Thanks again for your response!
We checked the caps on the crystal again. They have the right capacity (12 pF).
But it seems one of them wasn't soldered properly – after we resoldered it, we can now find the chips advertising packets!

Thanks again!

RE: nRF52 on custom board can receive BLE packets, but not send

ketiljo — Fri, 08 Mar 2024 13:09:23 GMT

What's the spec on the crystal? The caps needs to match the CL value of the crystal as follows:

Ccap = CL * 2 - Cpin, where Cpin = ~4 pF

RE: nRF52 on custom board can receive BLE packets, but not send

SenseJo — Thu, 07 Mar 2024 14:42:46 GMT

Hi ketiljo,

thanks a lot for your prompt response.

Sorry about the confusion about the crystal, it's just the label in the schematics which is wrong, but our boards are populated with 32 MHz crystals.

We soldered some load caps to the crystal and an inductor in series with L302 on a board, but unfortunately, nothing changed.

This is our matching network on the ANT pin:

RE: nRF52 on custom board can receive BLE packets, but not send

ketiljo — Thu, 07 Mar 2024 10:29:14 GMT

Is it correct that you're using a 40 MHz crystal?

This needs be 32 MHz, nothing else will work. You're missing the crystal load caps. Which, for a crystal with a CL value of 8 pGF, should be 12 pF each.

See the reference schematic:

https://infocenter.nordicsemi.com/topic/ps_nrf52840/ref_circuitry.html#unique_1496623802

Note that _all_ components here, except where noted, are mandatory. You're missing the 15 nH inductor in series with L302. The matching netwotk on the ANT pin must be there are well.