Measure current profile with an oscilloscope

An oscilloscope can be used to measure the average current over a given time interval and capture the current profile.

1. Prepare the nRF54LM20 DK as described in Set up the DK.
2. Mount a 10 Ω ±0.1% 0402 resistor to R15 which is located at the back of the nRF54LM20 DK.
3. Set the oscilloscope to differential mode or a mode that is similar.
4. Connect the oscilloscope using two probes on the pins of the P14 header, as shown in the following figure.
5. Calculate or plot the instantaneous current from the voltage drop across the R24 resistor by taking the difference of the voltages measured on the two probes.
   The voltage drop is proportional to the current. The 10 Ω resistor causes a 10 mV drop for each 1 mA drawn by the circuit being measured.

The plotted voltage drop can be used to calculate the current at a given point in time. The current can then be averaged or integrated to analyze current and energy consumption over a period.

Figure 1. Current measurement with an oscilloscope

To reduce noise, do the following:

• Use GND leads that are as short as possible.
• Use probes with 1x attenuation.
• Enable averaging mode to reduce random noise.
• Enable high-resolution function if it is available.

Use a minimum of 200 kSa/s (one sample every 5 µs) to get a reliable average current measurement.

To accurately measure the current consumption of the nRF54LM20 DK, configure the oscilloscope to display the full range of currents you want to measure in the selected time window. Adjust the vertical scale in the oscilloscope to cover the full range of currents without clipping. Leave a small margin at the top or bottom of the vertical axis. Use an oscilloscope with high dynamic range (16 bits or more) to measure both small and large changes in current accurately.