The TPS6213x enters its built-in power save mode seamlessly if the load current decreases. This secures a 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 happens within the entire regulation scheme and is seamless in both directions.

The TPS6213x includes a fixed on-time circuitry. An estimate for this on time in steady-state operation with FSW = Low is:

Equation 1.

For very small output voltages, an absolute minimum on time of approximately 80 ns is kept to limit switching losses. The operating frequency is thereby reduced from its nominal value, which keeps efficiency high. Also, the off time can reach its minimum value at high duty cycles. The output voltage remains regulated in such case. Using t_ON, the typical peak inductor current in power save mode can be approximated by:

Equation 2.

When V_IN decreases to typically 15% above V_OUT, the TPS6213x does not enter power save mode, regardless of the load current. The device maintains output regulation in PWM mode.