Measurement Range Extension for PPK2 - Internal Resistance?

[Michael von Rueden]

Hi,

we would like to extend the measurement range of the PPK2 beyond 0.6 A in source meter mode, e.g. to measure the power usage of a Raspberry Pi. We know that this might be tricky, due to the automatic range adaptation - but we want to give it a try anyway :-)

To this end, I have two questions in advance:

1) What are the internal resistances of the PPK2? I tried to find it in the documentation, without success so far

2) Is it possible to log the switching of PPK2's measurement resistor value?

Thank you very much.

Best regards,
Michael

[Håkon Alseth]

Hi,

 

You should consider to use a multimeter that is rated for up to 3 A for such a task.

If you still plan to use the PPK2 for this purpose, please be aware that you are exceeding the el.spec. of the PPK2.

  

we would like to extend the measurement range of the PPK2 beyond 0.6 A in source meter mode, e.g. to measure the power usage of a Raspberry Pi.

You are going to starve the RPI, as it needs a PSU that is capable of providing up to 3 A (depending on the model).

In ampere meter mode, the PPK2 can handle up to 1 A, which _might_ work, depending on the RPI model that you're targeting.

 

1) What are the internal resistances of the PPK2? I tried to find it in the documentation, without success so far

These are trimmed per-device, to match the ranges:

https://docs.nordicsemi.com/bundle/ug_ppk2/page/UG/ppk/ppk_measure_resolution.html

But they do have an accuracy hit as well:

https://docs.nordicsemi.com/bundle/ug_ppk2/page/UG/ppk/ppk_measure_accuracy.html

2) Is it possible to log the switching of PPK2's measurement resistor value?

No, unfortunately not.

 

Kind regards,

Håkon

[Michael von Rueden]

Hi,

Thank you very much for the quick response. Maybe my first question wasn't clear enough :-)

I know that the PPK2 can only handle 0.6 A and adjusts the resistances to the measurement accuracy. We want to connect an adaptive shunt resistor (to be developed) in parallel as a current divider in order to increase the measurement range of the PPK2 to approx. 3 A (while reducing the measurement accuracy, of course) but to operate PPK2 within its specs.

To dimension the shunt resistors of the current divider, we need the values ​​of the internal resistances of the PPK2.

So could you provide the values of the internal shunt resistors for the following measurement ranges?

 200 nA–50 µA
 50 µA–500 µA
 500 µA–5 mA
 5 mA–50 mA
 50 mA–1000 mA

Regarding my second question: Is there a fundamental reason that this information is not available? Or is it "just" a software thing, in the sense that it might be provided in the future? For example the Joulescope JS220 Energy Analyser, which works kind of similarly, provides this information.

Best regards,
Michael

[Håkon Alseth]

Hi Michael,

 

My apologies, but we do not provide the details that you are asking for in our software, but the source code of the desktop application will give you insight of the default values/steps: https://github.com/NordicSemiconductor/pc-nrfconnect-ppk/blob/main/src/device/serialDevice.ts#L42

Michael von Rueden said:

Is there a fundamental reason that this information is not available? Or is it "just" a software thing, in the sense that it might be provided in the future?

There's no technical reason why it should be held back, but as mentioned; there are calibration data present on each device that also comes into play here.

 

Kind regards,

Håkon

[Michael von Rueden]

Hi,

Thank you very much for the information and the pointers to your GitHub-Repos. I think we can make it from there.

Cheers,
Michael

[hmolesworth]

This might help ..

// Resistor Rc for current sense is 1k0 in parallel with one or more of 110R, 11R0, 1R0 and 0R051
//
//              <- +ve Supply to DUT From VOUT                               External Battery +ve To VIN
//             +------------------------------+                             +-----------------------+
//             |                              |                             |                       |
//             |              +---------+     |                             |     +---------+       |
//             |              |     GND |     | VOUT                   VIN  |     | GND -ve |       |
//   +=========O=========+    |    +====O=====O=============================O=====O====+    |       | Battery
//   |        Vdd (+)    |    |    |    |     #----+                        |     |    |    |       | + 3 volts
//   |                   |    |    |    |     |    |Rc        AMPERE \      |     |    |    |     +-O-+
//   |                   |    |    |    |     |   +++                 \     |     |    |    |     |   |
//   |                   |    |    |    |     |   | |   +-----------O  O----#     |    |    |     |   |
//   | Device Under Test |    |    |    |     |   | |   |                   |     |    |    |     |   |
//   |       DUT         |    |    |    | 120k|   | |   |                   |120k |    |    |     |   |
//   |                   |    |    |    |    +++  +++   |   \  SOURCE      +++    |    |    |     |   |
//   |                   |    |    |    |    | |   |    |    \             | |    |    |    |     +-O-+
//   |                   |    |    |    |    | |   +----#--O  O-- PPK LDO  | |    |    |    |       | Gnd (-)
//   |                   |    |    |    |    | |                           | |    |    |    +-------+
//   |                   |    |    |    |    +++                           +++    |    |
//   |                   |    |    |    |     |                             |     |    |
//   |                   |    |    |    |     #-- VDUT                VIN --#     |    |
//   |                   |    |    |    |     |  Sense                Sense |     |    |
//   |                   |    |    |    |    +++                           +++    |    |
//   |                   |    |    |    |    | |                           | |    |    |
//   |                   |    |    |    |    | |                           | |    |    |
//   |                   |    |    |    |    | |                           | |    |    |
//   |                   |    |    |    |    +++                           +++    |    |
//   |                   |    |    |    |     | 30k                     30k |     |    |
//   |                   |    |    |    +--#--+                             +--#--+    |
//   |                   |    |    |       |                                   |       |
//   |                   |    |    |     =====      <<== Common Gnd ==>>     =====     |
//   |                   |    |    |      ===           (Common -ve)          ===      |
//   |        Gnd (-)    |    |    |       =                                   =       |
//   +=========O=========+    |    +===================================================+
//             |              |     PPK-II
//             +--------------+