High current consumption on nrf52 dk

[Michal]

Hi,

I have a beacon code for nrf51 that I wanted to port to nrf52. It uses app_timer, gpiote and adc. The power consumption in idle is ~30uA. Now I wanted to port this code to nrf52 but have problems with current consumption. What I see is that current is on const around 1mA level. I thought maybe I have done something wrong with SAADC so I removed it from code but result is about the same. I was stripping components one by one as I get to point where I have only for loop with __WFE() inside and I see 200uA !(softdevice present but not enabled) . Any idea what is wrong? Now I think that maybe some errata code is needed or maybe it is the errata code in startup causing troubles?

For measurment I used giant gecko with simplicty studio energy profiler.

Regards,

Michal

[Håvard]

Hello,

To verify that there is nothing wrong with the board itself, could you try to go to system-off? (Just copy the code below ) This should bring the consumption down to ~ 300 nA. Consumption around 200uA can indicate that the high frequency clock is running. Maybe I could see more of your code to verify it?

int main(void)
{
    NRF_POWER->SYSTEMOFF = 1;

    while (true)
    {
    }
}

[Michal]

I tired your code with systemOff and the result of consumption is around 200uA. Why would be hfclk running if I did not use it ? Any other ideas what can be wrong ?

[Håvard]

Hello, it should not be possible to draw that much current in system off, unless the chip or DK is faulty.

Are you using a DK, or are you on a custom PCB? Could there be some external component drawing power?

[Michal]

I am using nrf52 dk. I tried 2 different ones - both 200uA. On the segger there is note about version - one was 1.1.1 and second was 1.2.1 - these are production version not an engineering samples ? I dont have anything connected to dk. 

About my measurment setup - it works well, with nrf51 I am able to measure current around 20uA. 

[Håvard]

I have never tried the gecko simplicity studio energy profiler, but have you had a look at this guide?

https://devzone.nordicsemi.com/tutorials/b/hardware-and-layout/posts/current-measurement-guide-introduction

Could it be you are seeing aliasing in the sampling?

excerpt:

The nRF52 power supply uses auto-controlled refresh modes to maximize efficiency. What this basically means is that a capacitor is recharged regularly to provide power to the chip. The recharge off the capacitor happens during a very short time interval, and results in a high frequency peak in current. This peak is measured to be about 10 - 15 us long. In order to get the correct average current during these peaks, a sampling frequency corresponding to half the peak length is required. This results in a minimum frequency of 200k samples per second (1 sample every 5 us).

[Michal]

I dont see any aliasing. I will try different measuring methods and come back with results. It is quite possible that the way I measured current on nrf51 is not valid for nrf52.

[Michal]

So it turns out that my measuring setup which was valid for nrf51 is not for nrf52. Doing measurment with ampere meter as described in guide showed values which are more accurate. Thanks Havard !