The TPS61022 operates at a quasi-constant frequency pulse width modulation (PWM) in moderate-to heavy load condition. Based on the input voltage to output voltage ratio, a circuit predicts the required on-time of the switching cycle. At the beginning of each switching cycle, the low-side NMOS FET switch, shown in Functional Block Diagram, is turned on. The input voltage is applied across the inductor and the inductor current ramps up. In this phase, the output capacitor is discharged by the load current. When the on-time expires, the main switch NMOS FET is turned off, and the rectifier PMOS FET is turned on. The inductor transfers its stored energy to replenish the output capacitor and supply the load. The inductor current declines because the output voltage is higher than the input voltage. When the inductor current hits a value that is the error amplifier's output, the next switching cycle starts again. The error amplifier compares the feedback voltage of the output voltage with an internal reference voltage; its output determines the inductor valley current in every switching cycle.

In light load condition, the TPS61022 implements two operation modes (power-save mode with PFM and forced PWM mode) to meet different application requirements. The operation modes are set by the status of the MODE pin. When the MODE pin is connected to logic low, the device works in the PFM mode. When the MODE pin is connected to logic high, the device works in the forced PWM mode.