When the MODE/S-CONF pin is configured for auto PFM/PWM mode, power save mode is allowed. The device operates in PWM mode as long 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 conduction mode (DCM). This happens if the output current becomes smaller than half the ripple current of the inductor. Power save mode is entered seamlessly to make sure there is high efficiency in light-load operation. The device remains in power save mode as long as the inductor current is discontinuous.

In power save mode, the switching frequency decreases linearly with the load current maintaining high efficiency. The transition into and out of power save mode is seamless in both directions.

The TPS629203 adjusts the on time (TON) in power save mode, depending on the input voltage and the output voltage to maintain highest efficiency. The on time in steady-state operation can be estimated as:

With the MODE/S-CONF pin set to 1.0-MHz operation:

Equation 4.

With the MODE/S-CONF pin set to 2.5-MHz operation:

Equation 5.

Using TON, the typical peak inductor current in power save mode is approximated by:

Equation 6.

The output voltage ripple in power save mode is given by Equation 7:

Equation 7.