Power Profiler Kit 2 Reading Low and High

RE: Power Profiler Kit 2 Reading Low and High

Einar Thorsrud — Fri, 30 Aug 2024 10:53:47 GMT

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.

RE: Power Profiler Kit 2 Reading Low and High

edmcnicholas — Wed, 28 Aug 2024 17:26:35 GMT

RE: Power Profiler Kit 2 Reading Low and High

edmcnicholas — Wed, 28 Aug 2024 17:25:04 GMT

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

RE: Power Profiler Kit 2 Reading Low and High

Einar Thorsrud — Wed, 28 Aug 2024 14:10:14 GMT

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.

RE: Power Profiler Kit 2 Reading Low and High

edmcnicholas — Wed, 28 Aug 2024 12:53:25 GMT

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.

RE: Power Profiler Kit 2 Reading Low and High

Einar Thorsrud — Wed, 28 Aug 2024 07:17:13 GMT

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).

RE: Power Profiler Kit 2 Reading Low and High

edmcnicholas — Tue, 27 Aug 2024 15:22:49 GMT

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

RE: Power Profiler Kit 2 Reading Low and High

edmcnicholas — Tue, 27 Aug 2024 13:48:43 GMT

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.

RE: Power Profiler Kit 2 Reading Low and High

edmcnicholas — Tue, 27 Aug 2024 13:44:57 GMT

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.

RE: Power Profiler Kit 2 Reading Low and High

edmcnicholas — Tue, 27 Aug 2024 13:42:31 GMT

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

RE: Power Profiler Kit 2 Reading Low and High

edmcnicholas — Tue, 27 Aug 2024 13:40:56 GMT

I am not using a resistor that is the voltage coming into the DUT.

RE: Power Profiler Kit 2 Reading Low and High

Einar Thorsrud — Tue, 27 Aug 2024 13:34:37 GMT

Hi,

I see the value is close to 3 V, so this cannot be the voltage drop across the resistor. Can you meaure the voltage drop across the resistor only? And what is the value of the resistor you are using? If you pic for isntance a 10 ohm resistor, we can easily calcualte the current by just dividing the voltage drop by 10 at any given point in the plot.

RE: Power Profiler Kit 2 Reading Low and High

edmcnicholas — Tue, 27 Aug 2024 13:13:21 GMT

RE: Power Profiler Kit 2 Reading Low and High

edmcnicholas — Tue, 27 Aug 2024 13:11:31 GMT

These cant be right as there is no way to be at 3uA with the circuit on. I do see alignment between pulses on the input voltage and current spikes match at 5.5ms intervals

RE: Power Profiler Kit 2 Reading Low and High

Einar Thorsrud — Tue, 27 Aug 2024 12:46:51 GMT

I see. Then based on the current information I do not see a good reason to doubt the measurments from the PPK. But if you want to digg deeper, measuring the voltage drop over a series resistor with an oscilliscope would be the next step. I would expect to see the same pattern as you see in the PPK plot. If not, there may be a need to look more closely at the PPK measurements.

RE: Power Profiler Kit 2 Reading Low and High

edmcnicholas — Tue, 27 Aug 2024 12:42:44 GMT

I was measuring the power profiler with known resistance and that gives fairly steady data. I could try using my scope but i have just been looking at rms for worst case.

The regulator we are using is TPS61099DRVR the frequency is 1-3mhz. There is a pfm light load mode. When in boost or pass through I see voltage spikes that sag the input voltage by over 0.1v

RE: Power Profiler Kit 2 Reading Low and High

Einar Thorsrud — Tue, 27 Aug 2024 07:23:16 GMT

[quote user="edmcnicholas"]I measured the device with several resistors and it was fine.[/quote]

Did you meassure the voltage drop over a series resistor? Was that located in the same place in the cuircuit that you measure current with the PPK2? Can you share the plot of the measurmenents you did over the resistor with an oscillioscope?

[quote user="edmcnicholas"]Will a boost regulator make the power profiler unstable?[/quote]

That is a possibility, particularily if the switching frequency is very high. Which boost converter do you use?

RE: Power Profiler Kit 2 Reading Low and High

edmcnicholas — Mon, 26 Aug 2024 18:45:22 GMT

The boost is operating in light mode so that might have some pulsing

RE: Power Profiler Kit 2 Reading Low and High

edmcnicholas — Mon, 26 Aug 2024 15:37:07 GMT

I measured the device with several resistors and it was fine. Will a boost regulator make the power profiler unstable?

RE: Power Profiler Kit 2 Reading Low and High

edmcnicholas — Mon, 26 Aug 2024 14:31:00 GMT

I have a fluke and all i am turning on is the amp circuit that i measured the current using the multimeter. THe fluke is actually quite quick and will show fluctuations on the bar graph at the bottom even if it does not show on the screen.

I also measured the voltage drop across the feed resistor into the amplifier that is 27.5uA so there is no way i should be seeing 3uA readings.

RE: Power Profiler Kit 2 Reading Low and High

Einar Thorsrud — Mon, 26 Aug 2024 14:15:34 GMT

How do you know taht it should be 100uA steady state? The multi meter will not show you short fluctuations over time? If you have an oscillioscope you could use for instance a 10 ohm resistor in series with the supply and measure the voltage drop over that to measure the current consumption over time without the PPK. Do you see the same current consumtpion pattern then?

RE: Power Profiler Kit 2 Reading Low and High

edmcnicholas — Mon, 26 Aug 2024 13:25:55 GMT

What i am asking is that if i know the measurement should be about 100uA steady state without much fluctuation as it is an amplifier circuits quiescent current how do i get a proper reading when I see that most of the time it is almost 0 and the spikes are not at my average current. if it is in 100k sample per second mode i would expect it to be properly sampling at that rate without just drastic fluctuations especially in ampere meter mode.

RE: Power Profiler Kit 2 Reading Low and High

Einar Thorsrud — Mon, 26 Aug 2024 13:17:41 GMT

Is the question how you can measure the avarage current during an interval? If so, you can select the range you want to measure and look at the average number (you get one both for selection and the whole window).

RE: Power Profiler Kit 2 Reading Low and High

edmcnicholas — Mon, 26 Aug 2024 12:46:25 GMT

so how would I get good measurements if this is the case?

RE: Power Profiler Kit 2 Reading Low and High

Einar Thorsrud — Mon, 26 Aug 2024 12:14:49 GMT

Yes, it would stil be the case, as the nRF itself use refresh mode when the current consumption is low. In this case the current consumption will be close to zero most of the time, except for when the regulator is on for a short time to charge up internal capacitors.