nRF5340 host used with nRF7002 must have an external HFXO

[Sebastian01]

Hello I am looking for some guidance.

I have not found a clear answer in the documentation, but should a nRF5340 host used with nRF7002 have an external HFXO?
We only use the nrf7002 for wifi, so there is no COEX defined. These pins are left floating.

The host nrf5340 interfaces with the nrf7002 wifi chip using high speed SPIM4.

[Samruddhi Jadhav]

Hi Sebastian,

HFXO is required for nrf5340 + nrf7002 for frequency accuracy and stability. In order to use the radio in nrf5340, it needs a high frequency clock that is stable and using HFXO also ensures timing precision. The HFXO operates at 32 MHz and the nrf5340 requires 32 MHz crystal operation. 

Best Regards,

Samruddhi

[Sebastian01]

Hello Samruddhi, thank you for the answer.

Maybe I am misunderstanding how the radio works in nrf5340, but I thought the nrf5340 radio would not be in use when we only enable wifi via the nrf7002.
Is the radio still used for interfacing with the nrf7002 with COEX disabled?

[Samruddhi Jadhav]

Hi,

The nrf5-series requires HFXO for radio. However, when using SPIM, the HFXO also has to be running in order to get highest accuracy. SPIM4 is quite fast. Have you tried using a lower speed like 1MHz? This is just in case there's an issue regarding speed or drive-strength of the SPI lines. 

Best Regards,

Samruddhi

[Sebastian01]

I haven't tried anything yet. The question is more related to design choice, if we need to include a HFXO in our design that uses wifi via the nrf7002 and have Bluetooth and COEX disabled.

But if the SPIM4 will request the HFXO instead of a high speed internal clock, we will include a HFXO crystal in our design.

[Samruddhi Jadhav]

Hi,

For SPIM4, there is no direct dependency on HFXO unless you plan on using the radio or USB then you will need it. In nRF5x designs, you do need to normally include HFXO as it is a listed required component. 

Best Regards,

Samruddhi