The TPS6214x 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.

TPS6214x includes a fixed-on-time circuit. 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 about 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 VOUT, the TPS6214x does not enter power-save mode, regardless of the load current. The device maintains output regulation in PWM mode.