Anomalous high current transients every 8 sec in BLE sleep mode -nRF52832

RE: Anomalous high current transients every 8 sec in BLE sleep mode -nRF52832

Simonr — Wed, 06 Apr 2022 13:16:06 GMT

Okay, I was just confused as the defines were stated to be 0, but yes, it seems to be the RC oscillator. And by setting the calibrations to 0, you should be able to only calibrate manually. But this is not recommended for most applications.

Best regards,

Simon

RE: Anomalous high current transients every 8 sec in BLE sleep mode -nRF52832

dbur — Wed, 06 Apr 2022 07:50:56 GMT

JKe is our SW developer. We do not have an external oscillator, though it seems like maybe in our next rev we should add one. There is also not one on board of the Laird BL652 module we are using. From 5.2.1 of the Laird data sheet:

"To keep the on-chip 32.768 kHz RC oscillator within ±250 ppm (which is needed to run the BLE stack) accuracy,
RC oscillator needs to be calibrated (which takes 16-17 mS) regularly. The default calibration interval is eight
seconds which is enough to keep within ±250 ppm. The calibration interval ranges from 0.25 seconds to 31.75
seconds (in multiples of 0.25 seconds) and configurable via smartBASIC command at+cfg210."

This sounds exactly like what we are seeing.

Since we sleep and do nothing except after a button press to send a beacon it seems we could set the interval long and just do an extra RC osc cal whenever a button press occurs, if there is a way to manually invoke it.

Thanks for that link to the power optimization article. I think that will help.

RE: Anomalous high current transients every 8 sec in BLE sleep mode -nRF52832

Simonr — Wed, 06 Apr 2022 05:52:08 GMT

Are you a colleague of dbur? If this is not the case and NRF_SDH_CLOCK_LF_SRC is set to 1 in your sdk_config.h, then I don't think this is the RC oscillator. Do you have an external 32.768 kHz crystal mounted on your BLE device or not? If you do, this shouldn't be the RC oscillator waking up and drawing the excess current. You can check out this guide where my colleague explains how to optimize power consumption on nRF52 designs.

Best regards,

Simon

RE: Anomalous high current transients every 8 sec in BLE sleep mode -nRF52832

JKe — Tue, 05 Apr 2022 16:50:46 GMT

Both of the NRF_SDH_CLOCK defines you mentioned are set to 0 in the sdk_config.h file.

RE: Anomalous high current transients every 8 sec in BLE sleep mode -nRF52832

JKe — Tue, 05 Apr 2022 16:45:26 GMT

We are using version nRF5 SDK16.0.

RE: Anomalous high current transients every 8 sec in BLE sleep mode -nRF52832

Simonr — Tue, 05 Apr 2022 08:06:09 GMT

In order to make sure the oscillator doesn't drift too much to break with the BLE specification, it is strongly recommended that the calibrations occur at least every 8 seconds. You're free to play around with the NRF_SDH_CLOCK_LF_RC_CTIV and NRF_SDH_CLOCK_LF_RC_TEMP_CTIV defines in the sdk_config.h of your project (I assume you're using the nRF5 SDK) which is where you set how often SoftDevice calibration should be done when the RC oscillator is in use. Setting both to 0 should disable the calibration entirely, but then you won't be able to do much in terms of BLE.

The RTC is the Real Time Counter module, and not the same as the RC oscillator which is one of the LF clock sources you can use for the nRF52832. I also see you're referring to some very old documentation, and I recommend you refer to the latest version of the nRF52832 product specification (v1.8)

I see that you tried uploading a picture or link as well, but this seems to be broken as we're not able to open it on our end.

Best regards,

Simon

RE: Anomalous high current transients every 8 sec in BLE sleep mode -nRF52832

dbur — Mon, 04 Apr 2022 21:30:52 GMT

Is there a way to disable that completely? Or maybe only allow the cal to occur at other longer intervals or to occur only when specifically invoked? I see in nRF52832_OPS_v0.6.3.pdf 23.11 the RTC is only supposed to use 0.1uA, which would be acceptable, but would like to reduce or eliminate the amount of power used by the cal cycle. (assuming that is what the issue is)

RE: Anomalous high current transients every 8 sec in BLE sleep mode -nRF52832

Simonr — Mon, 04 Apr 2022 13:17:46 GMT

This sounds very much like the internal 32.768 kHz RC oscillator waking the HF clock up for calibration every 8 seconds. The RC oscillator will be used if the optional external 32.768 kHz crystal is not in the design of your device. I know the Laird modules don't come with these at least, but it should be possible to add one if you are developing a PCB design yourself.

What SDK and SDK version are you using for your project?

Best regards,

Simon