Using an oscilloscope for current profile measurement

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

1. Mount a 10 Ω resistor on the footprint for R64.
2. Connect an oscilloscope in differential mode or similar with two probes on the pins of the P22 connector as shown in the following figure.
3. Calculate or plot the instantaneous current from the voltage drop across the 10 Ω 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

Some tips to reduce noise:

• Use probes with 1× attenuation
• Enable averaging mode to reduce random noise
• Enable high resolution function if available

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