I want to implement the Inverting Buck-Boost function on this board. The input voltage is 5V, the output voltage is -6.6V, and the output current is 800mA. My main change is to connect a 1uF between Vin and GND (Vout before the change). Electrolytic capacitor, the function has been realized, but the phenomenon of ripple instability is found, as shown in the figure.
I think this is caused by the loop stability, but I recalculated the comp compensation according to the technical manual, but the situation has not improved, or because it is buck-boost, the formula should be changed, I hope you can tell me the exact original parameters How big should you choose
The parameters I changed before are as follows: R4=16Kohm c5=10uF c8=36pF