Figure 7-11 shows an equivalent model for the TPS54388C-Q1 control loop, which one can model in a circuit-simulation program to check frequency response and dynamic load response. The error amplifier is a transconductance amplifier with a g_m of 245 μS. One can model the error amplifier using an ideal voltage-controlled current source. The resistor R0 and capacitor C0 model the open-loop gain and frequency response of the amplifier. The 1-mV ac voltage source between nodes a and b effectively breaks the control loop for the frequency-response measurements. Plotting a over c vs frequency shows the small-signal response of the frequency compensation. Plotting a over b vs frequency shows the small-signal response of the overall loop. Check the dynamic loop response by replacing R_(L) with a current source that has the appropriate load-step amplitude and step rate in a time-domain analysis.

Figure 7-11 Small-Signal Model for Loop Response