Non-obvious power problem

RE: Non-obvious power problem

Moritz — Fri, 18 Aug 2017 16:05:28 GMT

Could this (entering debug mode unintentionally) also happen on a nrf52832? Looking into the NRF52-Product Spec at Debug and Trace it seams unlikely with the internal pullups/pulldowns. Any way we have experienced something quite similar in our preproduction run. 3 of 100 devices had a completely empty battery after 2 weeks. What I found out in the meantime is that we compiled the software with CONFIG_GPIO_AS_PINRESET, but have left the reset pin floating. Could this cause a higher current consumption in any way?

RE: Non-obvious power problem

Stefan Birnir Sverrisson — Tue, 13 Sep 2016 09:34:01 GMT

That is correct. I don't know any other method to enter debug mode than is described in section 11.1.2 in the nRF51 Series Reference manual 3.0, i.e. via the debug pins.

RE: Non-obvious power problem

John — Mon, 12 Sep 2016 12:29:19 GMT

Once again you have proven why you are over 14,000 reputation points. We ran units through the final production steps until we detected one that was in a high power state. We were able to remove the unit from its case very carefully and get it on a multi meter to measure power. When it was supposed to be in system idle mode it was burning 1.2mA, an hour later when it went into system off mode, power consumption jumped to 4-5mA. Clearly it was running with debugging enabled.

One question I have been asked and have answered no to with 99% confidence is that the only way into debug mode is via the pins. There is no way to enter debug mode programatically in the FW?

RE: Non-obvious power problem

Stefan Birnir Sverrisson — Thu, 08 Sep 2016 15:32:49 GMT

In system off, it is much simpler to get low current consumption, as entering system off disables all peripherals and the only way to wake up from system off is with a reset, assert on sense enabled pin, or with low power comparator. In the nRF51 Series Reference manual 3.0, section 11.1.2, it says:

If the device is in System OFF mode, entering into debug interface mode will generate a wakeup.

So if you are in system off and there is noise on SWDCLK pin, it can cause the chip to wake up and enter into debug mode with ~1mA current consumption. That is the most likely explanation I would think, as the battery is depleted in two weeks. So I would suggest to put 470ohm external pulldown resistor on SWDCLK pin

RE: Non-obvious power problem

John — Thu, 08 Sep 2016 12:12:03 GMT

Thanks Stefan, I was not aware of that. I'll have the HW guys check on that. For completeness sake, I'll attach the schematic (it's not a complicated board by any means).

Also I wanted to note that this is the first time we have used System Off instead of the System On Idle mode for low power. Additionally it is the first time we have used the sd_power_pof_* API's with the threshold set to 2.1V. I'm not sure if there are any rookie mistakes we could be making with either of those functionalities.

RE: Non-obvious power problem

Stefan Birnir Sverrisson — Thu, 08 Sep 2016 07:31:34 GMT

Hi John

Are you aware of the behavior of the debug pins?