In the forced PWM mode, the TPS61022 keeps the switching frequency constant in light load condition. When the load current decreases, the output of the internal error amplifier decreases as well to keep the inductor current down and deliver less power from input to output. When the output current further reduces, the current through the inductor decreases to zero during the off-time. The high-side P-MOSFET is not turned off even if the current through the MOSFET is zero. Thus, the inductor current changes its direction after it runs to zero. The power flow is from output side to input side. The efficiency is low in this mode. But with the fixed switching frequency, there is no audible noise and other problems which might be caused by low switching frequency in light load condition.