16MHz Crystal Current with SoftDevice

RE: 16MHz Crystal Current with SoftDevice

FormerMember — Thu, 02 Feb 2017 11:31:28 GMT

1) When the softdevice is enabled, it will turn off the HFCLK (HFXO) when when it has finished the radio operation. And that can collide with your requirements for the timer? Your timer needs to run off the HFXO, right? To make sure that the HFXO is not turned off by the softdevice, you should turn it on before enabling the softevice:

NRF_CLOCK->TASKS_HFCLKSTART = 1;
// wait for HFCLK to start
ble_stack_init();

The HFXO should then go into standby mode when it is not being used.

2) I think you would need to use nrf_drv_disable(..) (NRF_TIMER->TASKS_SHUTDOWN) to "release" the HFCLK, because it is needed for the chip to enter system ON.

3) Yes, the crystal will use "startup-current" for "startup-time" time. The crystal specific characteristics will affect the startup-time of the crystal.

RE: 16MHz Crystal Current with SoftDevice

FA — Fri, 27 Jan 2017 18:33:59 GMT

Can you please provide a clear answer to item 1, and confirm if 2&3 are correct (example was provided just to show what the blocks that I need are):

1- When Softdevice is enabled, can we expect the same automatic procedure of putting HFXO into standby or we have to use sd_clock_hfclk_release and do it manually? (please put aside whatever extra power is in standby, does the system put the HFXO in standby with SD enabled or not?)

2- My understanding is that"STOPPING the timer" is enough to tell the system that HFCLK is no longer needed. Is this true? or we should do some other things like disabling the timer interrupt or...

3- Based on Table 22, the startup current for 16MHz XO is 1.1 mA. I assume this current is drawn during the whole startup time of 800usec.

RE: 16MHz Crystal Current with SoftDevice

FormerMember — Fri, 27 Jan 2017 12:17:30 GMT

Okay, I see. I would recommend you to use the 32 MHz crystal (HFXO) during the 50 ms timing. During the 450 ms, I would recommend you to turn off the HFXO, and turn it on approximately 1 ms before the next time you need it. Having the HFXO in standby mode for 450 ms will use quite a bit of extra current.

RE: 16MHz Crystal Current with SoftDevice

FA — Thu, 26 Jan 2017 15:05:29 GMT

Ok, maybe I should clarify more. Due to my application needing more accuracy in time I HAVE to turn on the timer and use the HFCLK. So, please assume that due to whatever reason, we need to run the timer. In this case what will be the answer?

RE: 16MHz Crystal Current with SoftDevice

FormerMember — Thu, 26 Jan 2017 10:21:53 GMT

The RTC uses the LFCLK, so there is no need to start the HFCLK when using the RTC. When the softdevice is enabled, the LFCLK will run all the time, so no additional timer needs to be started to use the RTC.