The TPS6215x 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.

TPS6215x includes a fixed on-time circuitry. An estimate for this on-time, in steady-state operation with F_SW = 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 cases. Using t_ON, the typical peak inductor current in power-save mode is approximated by:

Equation 2.

When V_IN decreases to typically 15% above V_OUT, the TPS62150x device does not enter power-save mode, regardless of the load current. The device maintains output regulation in PWM mode.