The TPS61299x/xA 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 350mA and adjusting the valley current of this inductor depending on the output load. Since 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. 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. Once the output voltage exceeds a setting threshold (Vout_target + 50mV in normal mode and Vout_target + 25mV in fast load transient mode), the device stops switching and goes into a sleep status. In sleep status, the device consumes less quiescent current, 95nA. The boost converter resumes switching when the output voltage is below the setting threshold ( Vout_target + 25mV in normal mode and Vout_target + 10mV in fast load transient mode). The device exits the Burst mode when the output current can no longer be supported in this mode.

Figure 7-2 Control Modes under Different Load