In the diagram above, the x-axis shows the load current(mA) of the negative voltage of the AMOLED display. The y-axis shows the overall efficiency, which is the total output power divided by the total input power from a 3.7V input. When the display screen is completely dark, the OLED display unit does not emit light. But partial of its driving circuit is still active, meaning there is a certain basic consumption. As the load current increases, all driving circuit starts functioning, which means more total power consumption but reduced proportion of basic consumption. The RT4730’s efficiency performs better as load current increases.
Regarding Richtek’s power solution for portable AMOLED displays, the efficiency performance is significantly better than the RT4730. Unlike the RT4730 which has two power stages, this solution only has one power stage for single power conversion. The diagram below shows its efficiency under different load current.