initialized peripheral current draw after uninitialized

RE: initialized peripheral current draw after uninitialized

Vidar Berg — Sat, 19 Sep 2020 05:53:12 GMT

Thanks for confirming. So I would have expected the current draw to be 0.4 uA if it was isolated to the nRF device. The chip is nearly powered off in this mode so peripherals and clock sources are all automatically powered down by the system. The only two things the application should make sure of before entering system off is that there are no ongoing DMA transactions and to re-configure used IOs if necessary (GPIO settings are retained in system OFF).

Do the external sensors have inputs that may become floating? I'm wondering if the leakage may possibly be caused by that? It's ok to leave nRF IOs floating when they are configured to their reset state (input/disconnect) but other chips may require a constant pull-up, etc. If the i2c bus doesn't have external pull-ups mounted, maybe you can try to enable the internal pull-ups on the nRF before entering sleep and see if that helps.

RE: initialized peripheral current draw after uninitialized

matty — Fri, 18 Sep 2020 14:58:48 GMT

Thank you. In the quoted sentence, peripheral devices means the external sensors. Yes, they are always powered.

So, even if I leave TWI initialized and enabled, TWI and the resources it uses would be shutdown as soon as I enter system off? In system off, the nRF52840 isn't using any thing, In fact, by entering system off I can't inadvertently leave any nRF52840 resource/peripheral running?

[quote userid="4240" url="~/f/nordic-q-a/66054/initialized-peripheral-current-draw-after-uninitialized/270342"](i.e assuming no IO or peripheral initialization, just entering system OFF).[/quote]

Does my code snippet contain IO or peripheral initialization? I suppose the #include could eventually lead to IO or peripheral initialization. Although in this case I don't think it does. What I'm trying to get at is if I were to run just the following code

int main(void)
{

    NRF_POWER->SYSTEMOFF = 1;

    for (; ; )
    {
        __WFE();
    }

}

I should see a more or less flat line on my Otii at about 0.4 uA, given an ideal world. Anything more than 0.4uA is an indication of current use by the rest of the board? The nRF52840 is consuming 0.4uA, (I would add that the nRF52840 is part of a BMD340).

RE: initialized peripheral current draw after uninitialized

Vidar Berg — Fri, 18 Sep 2020 13:04:12 GMT

Hello,

[quote user=""]That indicates the peripheral devices are consuming power and need to be initialized and put to sleep.[/quote]

Just to confirm, is this referring to external sensors, or on-chip peripherals. And it if it's external sensors, are they always powered? I'm basically asking if there is a chance you may have leakage current going through these.I would expect the current going into the nRF52840 to be around 0.4 uA with the code snippet you posted (i.e assuming no IO or peripheral initialization, just entering system OFF).

The TWIM should not impact the base current once all transactions are completed. The peripheral should be powered down automatically by the power management unit. That's also my experience.

Best regards,

Vidar