Both TPS568230 and TPS56837 have On-time Extension function, but their implement is different.

The OTE of TPS568230 is decided by its duty cycle. When the 1.2 < VIN/VOUT ≤ 1.6, the TON will be extended one time interval. When the VIN/VOUT ≤ 1.2, the TON will be extended two time intervals. Thus it would lead to a sudden change of frequency during OTE operation.

The OTE of TPS56837 can slow down its frequency smoothly during OTE operation, which lead to a better performance during OTE operation.

Figure 4-7 provides a frequency changes with duty cycle of both TPS568230 and TPS56837.

For TPS568230, due to the on-time and frequency sudden change, the output voltage would have a transient process at the boundary of its OTE condition. On the other hand, during OTE process, the frequency of TPS56837 would change smoothly and have a better line transient performance.

Figure 4-8 and Figure 4-9 shows the line transient performance under large duty condition. Obviously we can see TPS568230 has about 12mV voltage overshoot at the two boundaries while TPS56837 doesn't.