The TPS61099x boost converter is controlled by a hysteretic current mode controller. This controller regulates the output voltage by keeping the inductor ripple current constant in the range of 300mA and adjusting the offset of this inductor current depending on the output load. Because the input voltage, output voltage and inductor value all affect the rising and falling slopes of inductor ripple current, the switching frequency is not fixed and is determined by the operation condition. If the required average input current is lower than the average inductor current defined by this constant ripple, the inductor current goes discontinuously to keep the efficiency high under light load condition. Figure 7-1 shows the hysteretic current operation. If the load current is reduced further, the boost converter enters into Burst mode. In burst mode, the boost converter ramps up the output voltage with several switching cycles. After the output voltage exceeds a setting threshold, the device stops switching and goes into a sleep status. In sleep status, the device consumes less quiescent current. The device resumes switching when the output voltage is below the setting threshold. The device exits the burst mode when the output current can no longer be supported in this mode. Refer to Figure 7-2 for burst mode operation details.

To achieve high efficiency, the power stage is realized as a synchronous boost topology. The output voltage V_OUT is monitored through an external or internal feedback network which is connected to the voltage error amplifier. To regulate the output voltage, the voltage error amplifier compares this feedback voltage to the internal voltage reference and adjusts the required offset of the inductor current accordingly.

Figure 7-1 Hysteretic Current Operation

Figure 7-2 Burst Mode Operation