When the MODE/S-CONF pin is configured for auto PFM/PWM with AEE mode, the TPS629206 provides the highest efficiency over the entire input voltage and output voltage range by automatically adjusting the switching frequency of the converter (see Equation 8). To keep the efficiency high over the entire duty cycle range, the switching frequency is adjusted while maintaining the ripple current amplitudes. This feature compensates for the very small duty cycles of high V_IN to low V_OUT conversions, which can limit the control range in other topologies.

Equation 8.

Traditionally, the efficiency of a switched mode converter decreases if V_OUT decreases, V_IN increases, or both. By decreasing the switching losses at lower V_OUT values or higher V_IN values, the AEE feature provides an efficiency enhancement across various duty cycles, especially for the lower V_OUT values, where fixed frequency converters suffer from a significant efficiency drop. Furthermore, when used with the recommended 2.2-μH inductor, the ripple current amplitudes remains low enough to deliver the full output current without reaching current limit across the entire range of input and output voltages (see Figure 8-4).

By using the same TON configuration (see Equation 9) across the entire load range in AEE mode, the inductor ripple current in AEE mode becomes effectively independent of the output voltage and can be approximated by Equation 9:

The TPS629206 operates in AEE mode as long as the output current is higher than half the ripple current of the inductor. To maintain high efficiency at light loads, the device enters power save mode at the boundary to discontinuous mode (DCM), which happens when the output current becomes smaller than half the inductor ripple current.