To evaluate the efficiency of the power train (device and inductor), it is important to measure the voltages at the correct location. This is necessary because otherwise the measurements will include losses that are not related to the power train itself. Losses incurred by the voltage drop in the copper traces and in the input and output connectors are not related to the efficiency of the power train, which should not be included in efficiency measurements.

Input current can be measured at any point in the input wires, and output current can be measured anywhere in the output wires of the output being measured.

Table 6-1 shows the measurement points for input voltage and output voltage. VIN and VOUT are measured to calculate the efficiency. Using these measurement points will result in efficiency measurements that excluded losses due to the wires and connectors.

For more accurate efficiency measurements of the power train, the voltage drop between the power train and the terminals should also be removed from the measurement. Using the test points in Table 6-2 will reduce these losses. To average the voltages at each test point so that only one meter is needed for PVIN and VOUT, add some resistance between the each test point and the meter. For the measurements taken in this user's guide, a 1.5-kΩ resistor was added in series with each test point. Using these test points reduced the measured power loss at 40 A load by approximately 0.15 W. This power is lost in the copper traces of the PCB.