Unexplained current draw from 51422 in System OFF

[Jason De Lorme]

Hi - I saw this post and I'm not sure how to add a clarifying question on to it: devzone.nordicsemi.com/.../

We have a similar problem in that we built our boards with the 12k pull-down resistor on SWDCLK. We're using the Dynastream N548 module so I'm still trying to identify exactly which 51422 version chip is in there, but our previous board used the QFAAE0 and I believe based on reading the PAN that based on that version we should NOT have the 12k pull-down resistor, correct?

We're seeing about 350μA draw in System OFF mode with simple code that does nothing other than turn on for a few seconds and then go to System OFF. It seems that 12k resistor should account for about 275μA, but that still leaves another 75μA. Are there other issues that could be attributable to this extra current draw? How low should we be able to get the chip? The Product Spec sheet says that Current in SYSTEM OFF, no RAM retention should be 0.6μA.

Thank you.

[Stefan Birnir Sverrisson]

Hi

That is correct, QFAAE0 version should not need the external pull-down resistor, it is provided internally on the SWDCLK pin.

The product spec specifies 0.6uA and that is approximately what you should see on your current meter.

After programming, make sure you power-reset the chip to get the correct current consumption reading. The chip is in debug mode after programming, which will consume high current, ~1mA.

To measure current, disconnect any external circuit from the GPIO pins and also the programmer from the SWD pins, in order to prevent any current leak.

To test the System Off and System On current consumption, try the standard powerdown examples given here, specifically written for this purpose.