With the MODE pin low, power save mode is active. In this operating mode, the switching activity is reduced and efficiency is maximized. If the mode pin is high, power save mode is disabled. The converter operates in continuous conduction mode.

In boost or in buck mode, the converter is operating up to the duty cycles with the respective minimum off times or on times. If the timing limits are reached, and the current is below the selected PSM entry threshold, the output voltage increases. As soon as this happens, the voltage regulation loop detects the increase and turns the device into a TI proprietary sleep mode as the energy consumed by the load is less than what the converter generates during switching. In this mode, both low sides are turned on to ensure the high-side gate voltage supply voltage for HB1 and HB2 are charged. Other internal circuits are partially turned off to reduce the current consumption of the converter to a minimum possible. In case the output voltage reaches the nominal output voltage set point, the switching activity starts again.

To avoid subharmonic frequencies due to repetitive entry and exit of the power save operation, the entry point is randomized between the nominal voltage and the maximum entry detection threshold of 1% above the nominal voltage.

In the buck-boost area where larger or smaller duty cycles is necessary, switching pulses are skipped. When necessary, the control initiates switching activities with a minimum time of state I or state III to maintain the inductor current as required by the voltage regulation loop.

Figure 7-5 Timing Diagram for the Power Save Mode