When you need to measure current in sub-Microampere range, and/or when you need to identify very short current spikes, classic multimeters won’t do. Such measurements are frequently necessary when analyzing and optimizing power consumption of battery- or solar-operated devices.
This is where tools like the Power Profiler Kit II (NRF-PPK2) come into play:
| Item | Classic Multimeter | Power Profiler Kit II |
|---|---|---|
| Resolution (Current) | 10uA | 200nA (0.2uA) |
| Resolution (Time) | 0.5s | 10uS (0.00001s) |
Overview
PPK2 produces high resolution graphs and offers a dynamic range from 200nA to 1A.
This device is available for around €80 which is surprising at first: professional multimeters with similar specs can cost way north of €2.000. One key difference is accuracy: PPK2 guarantees a 10% accuracy (and can measure 200nA +- 20nA) whereas high-end laboratory equipment has a margin of error in the range of 0.005-0.001%.
PPK2 is a very cost-effective tool for analyzing fast-changing currents across a huge dynamic range, and an ideal lab tool to analyze, understamd, and optimize battery- and solar-powered devices. It is not the right choice when you need scientific-grade accuracy.
Features
Here are the features:
- Flexible Power Source: powered by one or two Micro-USB cables, it can source up to 1A at configurable voltages in the range of 0.8V and 5V.
- Ampere-Meter: it can be used like a classic “Ampere-Meter”. Here, you provide the power source (i.e. a battery), and the unit measures the current. The power source must be in the range of 0.8V and 5V.
- Dynamic Range: It can accurately measure power consumption over the entire range typically seen in low-power embedded applications by auto-switching between five current measurement ranges for optimal resolution. Resolution varies between 200nA and 1mA depending on the measurement range, all the way up to 1A.
- High Sampling Rate: With 100kS/s, even small current spikes can be detected.
- Advanced Logic Analyzing: the unit comes with digital inputs that can be connected to GPIO outputs at the device under test. This enables code-synchronized measurements: your code sends markers by switching the GPIO to high or low, and these markers show up in the current measurement graph, enabling you to associate power consumption with particular code segments, helping to power-optimize code.
Hardware files can be downloaded as zip file and contain schematics, gerber files, and altium designer files.
Dynamic Range
Here are the five dynamically-controlled ranges:
| Range | Resolution | Accuracy |
|---|---|---|
| 200nA - 50uA | 200nA | 10% |
| 50uA - 500uA | 500nA | 10% |
| 500uA - 5mA | 5 uA | 10% |
| 5mA - 50mA | 50uA | 10% |
| 50mA - 1000mA | 1mA | 15% |
PPK2 automatically selects the range that is most appropriate for the measured current, and can switch between ranges dynamically during measurement. This way, you get the best possible resolution while being able to measure a huge range of currents, from Nano-Ampere to one Ampere.
This link is helpful: nordicsemi.com/startppk2. It is also printed onto the front cover of the device and brings you to a landing page where you find an overview plus a Where to Buy section listing resellers that currently have the unit in stock.
Package
Power Profiler Kit II ships in a small box and consists of the analyzer unit, two DuPont cables, and no Micro-USB power cable.
Connectors
A 4-pin cable is used for simple current measurements, and a 10-pin logic port cable can connect up to eight digital inputs to arbitrary GPIO outputs on the device under test to add markers to the log.
| Connector | Description |
|---|---|
| GND | Ground to device under test and external power supply (if any* ) |
| VIN | external power supply (Ampere meter mode only) |
| VOUT | positive output voltage to device under test |
| VCC | positive voltage from device under test (optional) |
| D0-D7 | eight digital input pins for logic analysis (optional) |
| USB DATA/POWER | Micro-USB to computer running nRF Connect For Desktop |
| USB POWER ONLY | Micro-USB to supply additional power (optional, Source meter mode only when requiring >500mA) |
| ON OFF POWER | Main power switch for unit |
To use the unit, you need to connect it via Micro-USB cable to a computer, and install the free cross-platform nRF Connect For Desktop software (available for Windows, Linux, and macOS). Within this software, you install the Power Profiler app.
nRF Connect For Desktop offers many more apps to perform additional diagnostics. For example, the Bluetooth Low Energy app helps in Bluetooth connectivity testing. These additional apps are beyond the scope of this article.
Initial Setup
Setting up PPK2 requires these steps:
- Download and install nRF Connect For Desktop software on your computer.
- Launch nRF Connect For Desktop, then install the Power Profiler App (which runs inside the main software)
- Connect PPK2 via Micro-USB cable. The cable needs to be connected to USB DATA/POWER, not USB POWER ONLY. Make sure the power switch on the unit is in ON position. A green light starts pulsating.
- Software may require a firmware update (“Device needs to be programmed”). Perform the firmware update as instructed.
- After the firmware update, the device may no longer be recognized. Reboot your computer.
Using PPK2
Here are the steps to launch PPK2 and perform measurements - assuming PPK2 has been connected to your computer as illustrated above, its power switch is in ON position, and it is showing a pulsating green light:
-
Launch nRF Connect For Desktop. Identify the app Power Profiler, and click Open.
-
In the upper left corner, click Select Device. A list of recognized devices slides in. Click PPK2.
-
A connection to PPK2 is established, and you see the Power Profiler User Interface.
Here is a Youtube video illustrating most of the steps.
If your PPK2 does not show up in the device list, it is either not connected, its power switch is not in the ON position, or it cannot be recognized yet by your computer. PPK2 should show a pulsating green light. If you can’t get the device to show up, reboot the computer. If you still can’t see the device, uninstall and reinstall the software, and make sure you are installing all parts of it.
Caveats
The nRF Connect For Desktop installer seems to be a mix of different software packages that execute in series. During installation, you may see different instances of installers pop up. Make sure you install all of the components.
PPK2 needs nRF Connect For Desktop which in turn needs J-Link which is installed as part of the installation package (unless you manually cancel its installation).
The J-Link installer offers to optionally install paid trial software. Accepting trial software is not required, so you can safely opt-out. Just make sure you do install the main J-Link software and do not accidentally cancel the J-Link installation altogether. If you did, then uninstall nRF Connect For Desktop, and start over again.
Introduction To User Interface
PPK2 is controlled via the left sidebar in the user interface. Here, you select its mode:
Two modes are available:
-
Source Meter: The unit supplies a configurable source voltage that can be used to directly power the device under test. When enabled, the unit blinks in red color, and a slider appears that sets the source voltage in a range of 800mV to 5V that is available at pin VOUT to power the device under test. The maximum current for this mode is 600mA and requires both Micro-USB cables to be connected.
-
Ampere meter: In this mode, the unit blinks in blue color. It now acts like a traditional Ampere meter: you supply the source voltage to the pin VIN (i.e. a battery). The device under test is powered via the VOUT pin. The maximum current for this mode is 1A.
In either mode, pin VOUT can be turned on and off with the slider Enable power output.
Performing Current Measurements
Here are the steps to perform a current measurement:
- Connect PPK2 and launch the software (see previous sections).
- Select the power supply mode you want to use. In Source meter mode, select the desired output voltage (see previous sections).
- Connect the power supply of your device under test to PPK2 (see below), and enable power via Enable power output.
- Set the desired sample rate, and start measuring the current consumption by clicking Start (see below).
Connecting Device Under Test
PPK2 acts as a monitored power supply and measures the current that is drawn from it. In other words: it acts as power supply for your device under test.
So the first step is to connect the power supply of your device under test to PPK2 using pins VOUT and GND (either one). Before you do, ensure this:
- Correct Voltage: when in Source meter mode, make sure you have set the appropriate output voltage. When in Ampere meter mode, make sure your own power supply is set to the correct voltage.
- Maximum Current: make sure your device under test does not draw more than 1000mA (Ampere meter mode) or 600mA (Source meter mode). If in Source meter mode, when requiring more than 500mA, you must attach a second Micro-USB cable to USB POWER ONLY.
VOUT sources power once you slide Enable power output into the ON position. It is ON by default.
Depending on the power supply mode you choose, these are the connections you need:
-
Source meter: connect VIN to the positive power supply pin of your device, and GND to its GND pin.
-
Ampere meter: in addition, connect your own power source to VIN and GND (either one). It must be in the range of 0.8V to 5V, and this voltage will power your device under test at VOUT.
Performing Test
To perform a current measurement, first make sure VOUT is enabled, and your device under test is powered: slide Enable power output to ON.
Next, select the desired sample frequency in the range of 1S/s to 100.000S/s. Optionally, set a duration for your measurement. By default, the measurement continues until you manually stop it.
Do not use the maximum sample frequency of 100.000 samples per second unless you really need it. If you just want to check power consumption over time, i.e. to test deep sleep modes, 100 Samples/second are more than enough. 100.000S/s produces huge amounts of data and can fill your hard drive quickly. This resolution is required only when you want to perform logic analysis (see below), or need to identify very short current spikes.
Click Start to start the measurement. The light on the PPK2 switches from pulse to solid.
You now see in real-time the current consumption in a graph on the right side. A sliding window constantly calculates average consumption, and PPK2 switches dynamically between five different current ranges, depending on the measured current.
Dynamic Range
The graph below is taken from a deep sleep test using a TTGO T-Display development board. You clearly see the current consumption during wake time and deep sleep in a highly dynamic range from as low as 373uA to as high as 240mA.
The resolution is constantly adapted to the measured currents. Below graph focuses only on the deep sleep phase and shows current consumption with a resolution of a few hundred nA:
Click Stop to stop the measurement. Data can be saved or else is discarded once you start the next measurement.
Using the Logic Port
For advanced analysis, your device can send logic level information to PPK2 via its GPIOs. Here is why this can be useful:
If you’d like to optimize power consumption, you may want to figure out which parts of your firmware code produces which current, or in other words: you want to find out how power-efficient your code is.
That’s especially useful if you have different ways to achieve the same goal in your code, and you’d like to know which way is most power efficient.
In order to synchronize your code with the PPK2 current graph, you can use up to eight GPIOs to send markers to PPK2: by switching a given GPIO to high when you enter a routine, and low when exiting it, you can then clearly see the power consumption generated just by this part of your code (assuming there are no other concurrent tasks running).
D0–D7 are sampled with 100 kHz frequency with a typical bandwidth of 50 kHz. According to Nyquist theorem, the minimum time interval you can pick up is 10us. If your code is executing faster, it cannot be reliably marked.
You can selectively enable and disable showing the digital channels in the lower left hand area of the PPK2 user interface.
Wiring
To add logic analysis, use the ten pin port in addition to the four-pin power port:
- Power Supply: connect VCC to the supply voltage of your device under test. This ensures the logic levels match. VCC must be in a range of 1.65V to 5.5V.
- D0-D7: connect up to eight GPIO outputs on your device to the D0-D7 inputs at the PPK2.
Troubleshooting
| Issue | Recommendation |
|---|---|
| Measurements unexpectedly fluctuate | Power consumption may be close to a dynamic range switching point, causing PPK2 to rapidly switch ranges. |
| Graph response is slow | Avoid USB hubs and docking stations. Connect PPK2 directly to computer |
| “Disk is full” warning | When free disk space falls below the disk full trigger (4GB by default), recording stops. Either clean up the hard drive to restore free disk space, lower the disk full trigger (not recommended), or store data on a different (but fast-enough) drive. In future measurements, you may want to reduce the sampling rate unless you require it. |
Internal Design
Overall system and interconnections:
Materials
PPK2 User Guide (v1.0.1)
PPK2 Hardware Files (v1.0.1)
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(content created Oct 07, 2024)