About MP2276 switching occurring twice

Dear supportmember,
This is a urgent project.

We have modified the evaluation board of MP2276 to create a negative power supply.

Vin = 3.8V
Vout = -3.3V
Iout = 1A (max)
fsw = 1MHz

Switching is stable when the output current is 0.35A or less.
When the output current becomes 0.35A or more, switching is performed twice or more, and the fluctuation of the output voltage becomes large.

circuit diagram


What is the cause of this phenomenon?

Is there a way to solve it?

Best regard.

Dear support member,
Could you teach the progress?

Best regard.

Dear support member,
This is a urgent.

Could you teach the progress?

Best regard.

Just some guy on the internet, I would try much larger Cout… The loop dynamics of a buck-boost converter are different than a buck converter.
The other thing is alter the value of the inductor. Try double or half?
Your schematic looks a little odd, the - 3.3 should be the old conventional ground shouldn’t it?

Dear jshannon,

Thank you very much for your reply.

Increased the capacity of the capacitor.
There was no change.

The capacitance of the inductor has been reduced.
There was no change.

The type of input capacitor 10μF has been changed from a ceramic capacitor to an electric field capacitor. The double pulse is gone.

Do you know the cause?

Best regard.