This IC is a boost converter. I am curious to understand how the input is stepped down using a boost converter.
Can someone explain the working and the graph too?
Why is there a flat line at -6V?
The IC has its own boost converter built in, so it can bias its internal high-side transistor. (This seems to be described in the data sheet.) An N-device in that function requires sufficiently high bias voltage to turn it fully On. The bias voltage needs to be greater than the power supply.
I believe the IC's output pin provides pulses of positive polarity at supply voltage. The output stage is configured as a buck boost converter.
sorry but I do not get your point, the MCCP16301 is clearly advertised as a buck/step-down converter and not as a boost converter. Further, your attached schematic doesn't follow the typical application shown in the datasheet at all. Have a look on the circuitry on pate 2 in the datasheet. Check the GND connection of your circuitry and how it is connected to the IC, as your attached Vout plot is measured with respect to GND.