A summary of the TPS56C231 load transient test conditions are provided in Table 2-1. The load transient is tested using TPS56C231EVM under 12 Vin, 1.2 Vout, 800 KHz switching frequency, Eco mode, output current from 0.2 A to 8 A with 2.5 A/us transient slew rate and 1 kHz toggling frequency conditions. Load transient performance is really related with inductor and output capacitor specs that are listed in Table 2-2.

To make the transient response measured effectively, two scope channels are needed. The first channel should be across the output of converter close to the regulation point. Measuring the output voltage away from the regulation point will cause a DC offset between heavy load and light load, due to voltage drop in the output cabling. It is extremely important to use proper probe measurement techniques. The tip and barrel probe method can make the ground loop as small as possible which is showed in Figure 2-2. The second channel should be the output current which is synchronous to the transient load change. The current measurement could be used as a trigger so that the resulting output voltage deviation could be seen clearly.

Using Tektronix DPO3054 oscilloscope and Chroma Eload 6314A with proper measurement method, load transient waveform in Figure 2-3 is obtained. Channel 1 is output voltage, using 1.2 V DC offset. Channel 4 is output current without offset.

Before saving data, measuring the real transient slew rate manually is necessary for correlation as the configuration transient slew rate of Eload and the real slew rate are usually not same. The real rising and falling slew rate are 0.68 A/us as Figure 2-4 shows.

To save waveform as CSV file, first click the oscilloscope bottom button of Menu, select Save Waveform button, then at the right side of the screen select all source and change the definition to CSV file. For DPO3054 oscilloscope, there is no storage inside and an USB is used to save the CSV file. Figure 2-5 is the flow chart of how to save scope waveform to CSV file.