The LM5123EVM-BST is typically configured to have fixed output voltage of 24 V. Figure 2-2 shows the resistor divider connection from the REF pin to the TRK pin that sets the output voltage to 24 V. R_VREFT is R24 and R_VREFB is R26 referring to the schematic.

Figure 2-2 Fixed Output Voltage Configuration

To dynamically change the output voltage, R_VREFT and R_VEFB are removed and the TRK pin voltage is driven directly to change the output voltage. See the data sheet for selecting the voltage range of the LM5123-Q1 and setting the TRK pin voltage to produce the desired output voltage. Figure 2-3 shows the configuration to change the output voltage dynamically. R_SET is R25 in the schematic.

Figure 2-3 Variable Output Voltage Configuration

To recreate the waveforms in Section 4.7, R_SET is set to be 24.9 kΩ and the TRK pin is driven between 400 mV and 550 mV, setting the output voltage to 24 V and 33V respectively.