The buck-boost is a popular nonisolated, inverting power stage topology, sometimes called
a step-up/down power stage. Power supply designers choose the buck-boost power stage
because the output voltage is inverted from the input voltage, and the output voltage can be
either higher or lower than the input voltage. The topology gets its name from producing an
output voltage that can be higher (like a boost power stage) or lower (like a buck power stage)
in magnitude than the input voltage. However, the output voltage is opposite in polarity from
the input voltage. The input current for a buck-boost power stage is discontinuous or pulsating
due to the power switch current that pulses from zero to IL every switching cycle. The
output current for a buck-boost power stage is also discontinuous or pulsating. This is
because the output diode only conducts during a portion of the switching cycle. The output
capacitor supplies the entire load current for the rest of the switching cycle.

download//understanding buck-boost power stages in switch mode power supplies