This design example is powered by a rechargeable battery that can be a building block in many portable applications. Noise-sensitive portable electronics require an efficient, small-size solution for their power supply. Traditional LDOs are known for their low efficiency in contrast to low-input, low-output voltage (LILO) LDOs such as the TPS7A13. Using a bias rail in the TPS7A13 allows the device to operate at a lower input voltage, thus reducing the voltage drop across the pass transistor and maximizing device efficiency. The low voltage drop allows the efficiency of the LDO to approximate that of a DC/DC converter. Equation 8 calculates the efficiency for this design.

Equation 8 reduces to Equation 9 because the design example load current is much greater than the quiescent current of the bias rail.