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  • Case ID: 349530
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nRF54L15 - System OFF : strange current peaks

Patrick49

I'm working with the nRF54L15-dk and with the system OFF sample available in https://docs.nordicsemi.com/bundle/ncs-latest/page/zephyr/samples/boards/nordic/system_off/README.html with SDK ver 3.0.2.

Following this post :  abnormal current peak when system off (0.6mA) 

I measured the current with a digit multimeter DMM7510 on the P6 header on the dev kit. With either the wake on pin (GPIO interrupt) or the GRTC wake up (period = 10 s), I'm seeing those strange current peaks after about 3-4 seconds. I run the program without RAM retention.

They appear irregularly and seem to be cap at about 750 µA. 

What could be the cause of those peaks and how to get rid to them ? 

Best regards, 

Patrick

  • +1 in reply to Patrick49

    As hakon says, the current peaks in question are caused by the hysteretic mode of the regulator and yes you can modify them slightly. Larger bulk capacitance slows down the charge pulse rate (as the bulk takes longer to discharge to the lower threshold) but increases the charging current spike. Lower capacitance increases the pulse rate and reduces the peak charging current. Frequent low current spikes may be preferable to slower higher current spikes; this is application dependent. Clearly the measurement tool sampling rate and frequency response will affect the reported current consumption, which may be unchanged but I would expect some difference. A better analysis is possible by for example replacing a coin cell with a fixed large capacitor which is charged to (say) 3.3V and the time taken to discharge to (say) 2.4V is accurately measured. Comparing the discharge times between different levels of bulk capacitance gives a better indication of true behaviour.

    Reducing bulk capacitance requires care to ensure voltage dips are not an issue on other areas; increasing is less of an issue other than extending hold-up time on battery removal which in itself may be an  issue.

    Edit: This is a Nordic doc on another part but it describes the basic hysteretic operation and the effect on measuring tools: nwp_034

  • 0 in reply to hmolesworth

    Hello, 

    Thanks for this detailled answer. It seems a bit complex to tune those peaks so we'll leave it like that I think. You are free to close this ticket.

    Best regards,

    Patrick

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