Figure 3-9 and Figure 3-10 show the response to load transients for both designs. The current step is from 0.75 A to 2.25 A and the current step slew rate is 1 A/µs. An electronic load is used to provide a DC 0.75-A load and the load transient circuit on the EVM is used to provide a 1.5-A step. The VOUT voltage is measured using TP10 for U1 and TP29 for U2.

When using the load transient circuit included on the TPS543320EVM, slowly increase amplitude of function generator for desired load step amplitude then vary the rise and fall times for the desired slew rate. The current for the load step can be sensed with the ISNS test point. The default resistors on the EVM provide a gain of 10 A/V. With this gain, a 1.5-A step will result in 150-mV at the ISNS test point.

Figure 3-11 and Figure 3-12 show the loop characteristics for both designs. Gain and phase plots are shown for V_IN voltage of 12 V and a 0.72-Ω or 1.32-Ω resistive load.

Figure 3-9 U1 Transient Response

Figure 3-11 U1 Bode Plot

Figure 3-10 U2 Transient Response

Figure 3-12 U2 Bode Plot

Figure 3-13 and Figure 3-14 shows the loop characteristics for U2 with the 3 different ramp settings.

Figure 3-13 U2 Loop Gain with Different Ramp Settings

Figure 3-14 U2 Loop Phase with Different Ramp Settings