8.4.1 Operation

The synchronous boost converter TPS61088-Q1 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 Functional Block Diagram, 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 it 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. Because 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 turns on again and the switching cycle is repeated.

In light load condition, the TPS61088-Q1 implements two operation modes, PFM mode and forced PWM mode, to meet different application requirements. The operation mode is set by the status of the MODE pin. When the MODE pin is connected to ground, the device works in the forced PWM mode. When the MODE pin is left floating, the device works in the PFM mode.