nRF52811 Clock Source

[Kaveh.M]

Is using a 32.768 kHz crystal for clock of nRF52811 chip, the option to achieve minimum power consumption? 

Is this only source of clock sufficient as the external clock? Or I have to also use 32MHz crystal with it? 

[Turbo J]

The 32 MHz quarz is required for bluetooth (and other radio) operation. I would also recommend it when using UART.

[Kaveh.M]

well, I dont see anywhere in the datasheet that external 32MHz crystal is mandatory to be used along with 32.768kHz crystal, if we are using an external clock source. 

I have used nRF82832 and nRF52833 in the past only using an external 32.768kHz crystal without any problem. The radio worked on those using only the low frequency external clock. 

[Håkon Alseth]

Turbo J said:

The 32 MHz quarz is required for bluetooth (and other radio) operation.

This is true.

Kaveh.M said:

well, I dont see anywhere in the datasheet that external 32MHz crystal is mandatory

You need to use an external 32 MHz xtal when using the RADIO peripheral.

HFXO requirements are listed here:

https://docs.nordicsemi.com/bundle/ps_nrf52811/page/clock.html#ariaid-title33

 

Kind regards,

Håkon

[Kaveh.M]

Ok. What if I dont want to use any external crystal? Can I just use internal sources for clock? 

What would be difference in power consumption in deep sleep mode when using internal clock sources compared with using 2 external crystal for 32kHz and 32MHz? 

[Håkon Alseth]

Kaveh.M said:

Ok. What if I dont want to use any external crystal? Can I just use internal sources for clock? 

Not if you need to use the RADIO peripheral. the 32 MHz xtal is a requirement for that.

Kaveh.M said:

What would be difference in power consumption in deep sleep mode when using internal clock sources compared with using 2 external crystal for 32kHz and 32MHz? 

You normally do not want the HFCLK to run during sleep, but the LFCLK would normally run. Here's the current consumption scenarios for running LFCLK (LFXO + internal LFRC):

https://docs.nordicsemi.com/bundle/ps_nrf52811/page/_tmp/photon/autodita/CURRENT/parameters.id_current_sleep.html

 

Kind regards,

Håkon

[Kaveh.M]

Thanks. Can I skip using LFXO and just use HFXO for all functions?

How the power consumption looks like in this case?  

[Håkon Alseth]

External 32k is optional, as shown here:

https://docs.nordicsemi.com/bundle/ps_nrf52811/page/ref_circuitry.html

 

Current consumption for both scenarios (ie. using internal 32k RC oscillator and external 32k quartz) is listed in the former link.