nRF52811 Clock Source

Question

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?

Håkon Alseth · Accepted Answer

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

Håkon Alseth · Answer

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

Håkon Alseth · Answer

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.

Håkon Alseth · Answer

Hi, 
 
 That is reference designs with DCDC converter enabled, and with traditional LDO regulator setup. Ie. the difference is in how you power the device. 
 
 Kind regards, 
 Håkon

nRF52811 Clock Source

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