The TPS61089x synchronous boost converter operates at a quasi-constant frequency pulse width modulation (PWM) in moderate to heavy load condition. Based on the V_IN to V_OUT ratio, a circuit predicts the required off-time of the switching cycle. At the beginning of each switching cycle, the low-side N-MOSFET switch, shown in Section 8.2, is turned on, and the inductor current ramps up to a peak current that is determined by the output of the internal error amplifier. After the peak current is reached, the current comparator trips, and turns off the low-side N-MOSFET switch and the inductor current goes through the body diode of the high-side N-MOSFET in a dead-time duration. After the dead-time duration, the high-side N-MOSFET switch is turned on. Since the output voltage is higher than the input voltage, the inductor current decreases. The high-side switch is not turned off until the fixed off-time is reached. After a short dead-time duration, the low-side switch is turned on again and the switching cycle is repeated.

In light load condition, the TPS61089 implements PFM mode for applications requiring high efficiency at light load. And the TPS610891 implements forced PWM mode for applications requiring fixed switching frequency to avoid unexpected switching noise interference.