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

[dbur]

We have a simple coin battery powered BLE device with a Laird BL652 module which has an nRF52832 chipset.

We have three buttons and set it up as low power as possible and only waking momentarily and sending a beacon on a button press.

In sleep mode we are measuring between 4-18uA current drain with no buttons pressed  (can we do better than this?). There is a problem though, every 8 seconds in undisturbed sleep mode we get a high current transient (700uA) that lasts 15 msec.  There are no other consumers of current in this circuit.

What can this be and can we stop it?  If so how?

Current is measured with a Fluke 87 DVM in uA range (100 ohm resistance).  The transient can be seen on this meter, but is more accurately characterized by measuring across a 100 ohm sense resistor with an oscilloscope.

[Simonr]

Hi

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

[JKe]

We are using version nRF5 SDK16.0.