quantifying PMIC overhead

[bios-bob]

actually a general question, though i'm working with the nPM2100 EK....

assume my target MCU operates "most efficiently" when supplied 1V8 -- expressing overall energy consumption in Joules....

but i'm using a 3V battery as my power source, hence i'll need to buck my voltage down to 1V8....

assuming i'm using a PMIC (like the nPM2100), how should i best capture the "real energy" consumed by this configuration....

using (say) a PPK, do i measure current "upstream" near my 3V source??? (or maybe i use the PPK to source 3V ???)

said another way, should i really be multiplying the Coulombs reported by the PPK by 3V to get my true energy consumption in Joules???

i have similar boards to the nPM2100 EK from other vendors and want to ensure i'm truly making an "apples-to-apples" comparison....

[Einar Thorsrud]

Hi,

using (say) a PPK, do i measure current "upstream" near my 3V source??? (or maybe i use the PPK to source 3V ???)

Both are possible with the PPK2.

said another way, should i really be multiplying the Coulombs reported by the PPK by 3V to get my true energy consumption in Joules???

The PPK2 shows the energy consumption as Coulombs as you write, to get it in joule you wuld need to claculate it by multiplying with the voltage.

[bios-bob]

forget about Joules for the moment.... my question is whether taking a current measurement upstream (at the 3V source) is the appropriate way to characterize the true power consumption of my system...

[Einar Thorsrud]

Yes, I would say that. If you are powering from a 3V battery, than the point you measure the current consumption of the whole system is where the battery is connected. This shows you the energy that is drawn from the battery.

[bios-bob]

ok....  i'm using the nRF54L15 as my target MCU -- which i can power directly at a range of voltages from 1V8 and up....  if i simply source 1V8 into the MCU, i get one set of current readings (which i can multiply by 1.8 to get joules)....  these results are quite good, in fact....

but again, i have a 3V source -- and can measure current consumption at the source....  in this case, i'd multiply by 3.0 to get joules....  my assumption is that "energy consumption" will presumably increase -- with the PMIC and its conversion being a big part of that equation....

at the same time, i can directly source 3V into my nRF54L -- which gives me a result that is less optimal than source 1V8 directly....  presumably there is some "on-chip" regulator which itself has overhead....

is that another fair comparison???  a 3V source directly into the nRF54L versus a 3V source into a PMIC that output 1V8 into my nRF54L....  same source voltage, but presumably different amounts of current consumption

[Einar Thorsrud]

Hi,

You are right that the nRF54L15 has an oboard DCDC buck converter as well, that regulates the interval volages, so the current consumption (but not energy consumption) is reduced with a higher supply voltage.

I am having problems understanding exactly what it is you want to achieve by this approach. If the goal is to quantify the PMIC overhead as you wrote in the initial post, you could measure the current and voltage into the nPM2100 and out of the nPM2100. Getting precise measurements here would be easiest with a fixed load. Note that the efficency of the nPM2100 is also described in the datasheet under Electrical specification for some combinations of input and output voltage, as well as curernt.