Power Profiler Kit 2 Reading Low and High

[edmcnicholas]

Hello I have a board that I am trying to profile with the power profiler kit 2 and the readings seem very wild.  I have a device that I know the base configuration with the sensors on is about 100uA measured with a fluke multimeter.  The issue I am seeing is that I am getting current levels between 2uA and 30mA with the BLE on and I can not get a steady state current.  This is the case with 2 separate PPK2 win Ampere Meter mode and Source Mode.  In source mode the current spikes show over 100mA.  it seems that the auto sensing is a bit haywire.  I am using the latest release of the power profiler sw.

From my measurements I should not be going below 20uA even with the sensors off and I am seeing sub 1uA for several mS even with a rate of 100k samples per second.

[Einar Thorsrud]

Hi,

It looks like you are seeing the LDO refresh mode. When the device is consuming low power, the regulator will be turned off most of the time, and only be enabled for a short while to optimizse average current consumption. You will see that as a sequence of spikes when you observe this witha  PPK or power analyzer or similar. When you measure the idle current with a multimeter you will not see this spikes, but instead see the average current.

[edmcnicholas]

But I am doing this in ampere meter mode. Would that still be the case.  I know I have an rms in one state of 150ua and it is flat since it is a sensor front end.

[edmcnicholas]

If it is in passthrough mode with voltage at 3.5V then I get something that looks normal with an average around 100uA.

[edmcnicholas]

I can walk the input voltage down to 3300mV but after that the regulator seems to go into drop or switch mode and the current is incorrect.

[edmcnicholas]

The sensor is buffered by an LDO for noise so that subsystem should always sus the same current.

3250mV is normal 100uA steady state

3200 mV 19.5uA with large pulses.

[edmcnicholas]

If I put it at 3000mV it goes crazy showing spikes to 150mA.

[Einar Thorsrud]

Hi,

I see. There is clearly an issue here, and that could reside in the PPK. However, I neeed to understand a bit more about the situation. Can you draw up how you measure and how the boost regulator and LDO and "sensor" is connected with the PPK (I assume you are measuring with the PPK before the regulators, but maybe that is wrong).

Also, as we suspect that the PPK is misbehaving, it would be very helpfull if you could measure the volgate drop over a series resistor with an osiclliioscope as mentionned before, as that is a simple way to see how the current flucuates over time. (Using the same principle as described here).

[edmcnicholas]

I can try doing the resistor later but for now power is being inspected at vbat con and gnd.  When I get below 3.3V then the boost turns on and the power profiler starts getting bad readings.  The radio is powered by VDD_MCU and the sensor is VDD_SENSE.

[Einar Thorsrud]

I see. Generally high frequency boost converters are difficult to measure and the PPK2 wills truggle with it, as you get a high frequency of pulses that covers all the ranges of the device in a very short time. Without seeing the plot I mentionned before I cannot conclude that it is the case, but it seems very likely. You could try to measure with large decoublig capacitors both on the source and output to reduce the large flucuations seen by the PPK.

[edmcnicholas]

3.4v Yellow is high side, Purple is low side and white is subtraction with 20ohm resistor.

[edmcnicholas]

3V

[Einar Thorsrud]

Hi,

Thank you for the plots. It is difficult to see all the details here, but it looks like this will be difficult for the PPK2 to measure. I see from the schematics that you have reverse protection, but if ther eis somehow a negative pulse on the PPK, that will also cause erronous measurements. So in shorts this seems like a cuircuit that cannot be properly measured with the PPK2.