Useage of HFCLK at SD110 startup

[victor]

Hello,

We are developing an application in which we have an NRF51822-CFAC with sd110 v7.0.0 together with very small energy allowances. Our problem is that we cannot get the NRF51822 to boot up and enable the softdevice without consuming the entire energy buffer that we have. When investigating what seems to be the culprit of the energy consumption we see that the NRF51822 enables the external 16 MHz clock for approximately 20 ms, during which the energy buffer is drained. My question is therefore if there is any way of starting up the softdevice without having it enabling the 16 MHz clock for such a long period of time?

Thankful for any advice.

[Stefan Birnir Sverrisson]

Hi

The softdevice itself should not take much time to enable. It can be however time consuming to enable the low frequency 32kHz external crystal clock source. When initializing the softdevice, you specify the 32kHz clock source to be either external crystal or the internal RC. Try to use the RC instead of the crystal in order to decrease the softdevice initialization time. If you want to use an external 32kHz crystal, you could start with manually enabling the crystal and go to sleep while you wait for it to start. Then you wake up again and initialize the softdevice.

[butch]

The nRF52 product spec under Clock/Electrical specifications does give the typical startup current and a typical startup time for the HFXO.