In this reference design, an auxiliary circuit was added to assist load transient test, as figure Figure 2-2 shows. The main part of auxiliary consists of a MOSFET and a 10mΩ SHUNT. An arbitrary waveform generator (like AFG3252) can be used to output a drive signal to MOSFET by connecting to J1 head pin.

Figure 2-2 Auxiliary Circuit

Notice, this circuit can be in parallel with 21A eLoad connected to the output as default. First, determine what voltage level through the gate corresponds to the different load levels (42A, 56A, 83A) and then use this info in writing the piecewise function in the ArbExpress software, as Figure 2-3 shows.

Figure 2-3 ArbExpress Equation Editor

After entering the piecewise into the equation editor in the software and set 100k points and 10M sampling rate, use the “Send to Arb” button when having laptop connected to the signal generator, to where the waveform looks like the ArbExpress internal simulation for the most part, as Figure 2-4 shows:

Figure 2-4 ArbExpress Internal Simulation Waveform

Using the Amphenol 523-095-850-206-024 on the Isense connector J2 or a differential probe across the sense resistor R49, one can test the current load. Using the Amphenol 523-095-850-206-024 on the Vsense connector J3, one can test the output voltage.

Through this method, one can get the load transient test results as Section 3.3.6 shows.