Using an oscilloscope for current profile measurement

Battery current profile can be measured using an oscilloscope with a differential probe across a shunt resistor. The voltage drop across the resistor will be proportional to the current flow. An oscilloscope can then measure the average current over a given time and capture the current profile.

1. Mount a shunt resistor within the acceptable range on the series resistor footprint for the signal of interest.
2. Connect an oscilloscope in differential mode or a similar mode with two probes on the pins of the measurement connector for the signal of interest.
   Note: Components for current measurement provides more information on the components used for the steps above.
3. Calculate or plot the instantaneous current from the voltage drop across the resistor by taking the difference of the voltages measured on the two probes. The voltage drop will be proportional to the current. For instance, a 100 mΩ resistor will cause a 0.1 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. VBAT current measurement with an oscilloscope

Some tips to reduce noise:

• Use X1 passive probes
• 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.