The AEE™ feature in the TPSM8290x provides highest efficiency over the entire input voltage and output voltage range by automatically adjusting the converter's switching frequency when 2.5 MHz is selected. This is achieved by setting the predictive off-time of the converter. The efficiency of a switched mode converter is determined by the power losses during the conversion. The efficiency decreases when V_OUT decreases and or V_IN increases. To keep the efficiency high over the entire duty cycle range (V_OUT/V_IN ratio), the switching frequency is adjusted while maintaining the ripple current. Equation 2 shows the relationship between the inductor ripple current, switching frequency and duty cycle.

Efficiency increases by decreasing switching losses and by preserving high efficiency for varying duty cycles while the ripple current amplitude remains low enough to deliver the full output current without reaching current limit. The AEE™ feature provides an efficiency enhancement for various duty cycles, especially for lower V_out values, where fixed frequency converters suffer from a significant efficiency drop. Furthermore, this feature compensates for the very small duty cycles of high V_IN to low V_OUT conversion, which limits the control range in other topologies.

When 2.5 MHz Auto PFM/PWM mode with AEE is selected, the efficiency can be better than the 1 MHz Auto PFM/PWM mode is some V_IN/V_OUT combinations at light loads conditions. For example at V_OUT=1.2 V and 15 V input, the efficiency is enhanced by almost 5% at 500 mA load and below.