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Measuring Ground current does not seem to match datasheet on STM32L476RG (Nucleo-L476RG)?

SWenn.1
Senior III

Hello...

I am using a Nucleo-L476RG dev board along with https://github.com/STMicroelectronics/STM32CubeL4 .  I have built the code for PWR_STOP1_RTC and am trying to measure ground current.  I have a 10 ohm resistor on the ground side of 3.2V battery.  I have removed JP6 and JP5 on the board.  I am using a USB PicoScope.  At the moment I have two issues:

1.  I load the FW onto the target but I don't understand why this FW does NOT seem to run if I don't keep the usb connected to the nucleo?  Why is this?  I would like to disconnect this as it is just a source of noise and I am getting no where near the approx.   4 uA - 20 uA the datasheet specifies.

2.  For some reason the ground current (when 1. above is connected) measures negative?  I can plug into a traditional scope and it is not negative.  I did calibrate probe and when connected to picoscope I did the autozero...Any thoughts here?  

Thanks

 

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