3.2 Bench Test Results

Figure 2-2 shows the implemented test schematics along with the selected ripple injection component values and feedback resistors. The simplified design approach is validated through frequency-domain and transient measurements, as shown in Figure 2-3.

Figure 3-1. MIC28515 Schematic Used for Bench Testing After Populating the Component Values Obtained From the Design Example

Figure 3-2. AC Analysis and Transient Response


Ripple Injection Components	ΔV_FB	F_C	Phase Margin	Undershoot	Response Time	Settling Time
C_INJ = 100 nF, R_INJ = 36k, C_FF = 4.7 nF	108 mV	31 kHz	87°	140 mV	16 us	80 us

The Bode plot indicates a crossover frequency of approximately 31 kHz, which is slightly higher than the earlier frequency-domain design, and a phase margin of about 87°, indicating a highly stable and well-damped control loop. The higher phase margin is a direct result of the larger C_FF value used in this approach, which shifts the second zero to a lower frequency and provides stronger phase boost around the crossover region. The measured feedback ripple ΔV_FB is approximately 108 mV, which falls within the recommended design range and confirms proper ripple injection.

The transient response further validates the design, with a load step from 2.5A to 5A showing an undershoot of approximately 140 mV, a response time of around 16 µs, and a settling time of about 80 µs. Compared to the optimized frequency-domain design, the transient response is slightly slower, which is expected due to the higher phase margin. This demonstrates the inherent trade-off in control loop design: while the simplified approach provides robust stability and ease of implementation, it may result in reduced transient speed. Overall, the results confirm that the simplified method offers a practical and reliable starting point for ACOT control loop design, especially when rapid design iteration is required.