nRF52840: At low temperatures I can't achieve the specified accuracy for the internal temperature sensor

RE: nRF52840: At low temperatures I can't achieve the specified accuracy for the internal temperature sensor

Frank Viganske — Fri, 22 Oct 2021 07:45:19 GMT

Hi Kenneth,

I changed the Firmware to switch over to the HFXO during the temperature measurement. Now at -40°C i get the result -41.5°C from a board that measured -53.75°C in my previous tests.

Problem solved. Thanks for your help.

Best regards

Frank

RE: nRF52840: At low temperatures I can't achieve the specified accuracy for the internal temperature sensor

Frank Viganske — Thu, 21 Oct 2021 08:56:16 GMT

Hi kenneth,

I inserted a debug print of the HFCLKSTAT at the beginning of the temperature measurement, and the value was 0x10000 (HFCLK running, but on the internal RC oscillator). So it seems that you're right, the inaccuracy might be caused by the incorrect clock source.

I'll try to change my firmware to keep the crystal oscillator running during the temperature measurement and see if that improves my accuracy.

Best regards

Frank

RE: nRF52840: At low temperatures I can't achieve the specified accuracy for the internal temperature sensor

Kenneth — Thu, 21 Oct 2021 07:48:16 GMT

[quote user="Frank Viganske"]i can do a debug print of some of the status registers for the HFCLK if that helps..[/quote]

That is a good idea. It may be that the radio protocol stack will start and stop the external HFCLK before and after the radio usage (this is the case even for Nordic softdevices, though there is an api that typically can be used to keep it ON all the time, which is what you want for this test).

Kenneth

RE: nRF52840: At low temperatures I can't achieve the specified accuracy for the internal temperature sensor

Frank Viganske — Thu, 21 Oct 2021 06:15:24 GMT

Hi Kenneth,

Sorry, i don't have the source code for starting the HF clock. We are using a third party radio protocol stack, and i only have that as a precompiled binary. The clock is controlled by this module. The radio was active and working fine during the test, so i'm sure that the HFCLK was running from the external crystal.

i can do a debug print of some of the status registers for the HFCLK if that helps..

Best regards

Frank

RE: nRF52840: At low temperatures I can't achieve the specified accuracy for the internal temperature sensor

Kenneth — Wed, 20 Oct 2021 11:58:42 GMT

Can you share the code snippet that startup the HFCLK before you execute temperature measurement? If you go to sleep, then you must startup the HFCLK every time you wakeup before you can do a temperature measurement.

Kenneth

RE: nRF52840: At low temperatures I can't achieve the specified accuracy for the internal temperature sensor

Frank Viganske — Wed, 20 Oct 2021 11:31:09 GMT

Hi Kenneth,

this has been taken care of. We have a 32MHz crystal connected to XC1 and XC2, and this was also selected as the HFCLK source during the test.

Best regards,

Frank

RE: nRF52840: At low temperatures I can't achieve the specified accuracy for the internal temperature sensor

Kenneth — Wed, 20 Oct 2021 11:13:19 GMT

Hi,

Make sure to check out:
https://infocenter.nordicsemi.com/topic/ps_nrf52840/temp.html

"To achieve the measurement accuracy stated in the electrical specification, the crystal oscillator must be selected as the HFCLK source, see CLOCK — Clock control for more information."

Best regards,
Kenneth