Dear,

customer design DCDC 5-9V input--> 5V/3A output , 

It's normal when with load,

but abnormal without load, the output fall down repetitive when input decrease to about 5.8V, the schematic is as follows:

and the follow is the input /output : upper line--input; lower line--output

and the follow is the output waveform in this situation:

please help to check is anything wrong with the design and how to solve this problem?

BTW, we find a similar question in Chinese, but no answer for years:

https://e2echina.ti.com/question_answer/analog/power_management/f/24/t/94798#pi58417=3

b/r

vincent