An oscilloscope can be used to measure both the average current over a given time
interval and capture the current profile.
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Mount a 10 Ω resistor on the footprint for R64.
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Connect an oscilloscope in differential mode or similar with two probes on the pins of the P22 connector as shown in the following figure.
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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 will be proportional to the current. The 10 Ω resistor will
cause 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.