Efficiency performance of Richtek power solutions in AMOLED applications

AMOLED displays have grown in popularity for a wide range of applications. Based on different requirements, displays in more pixels and higher brightness require more power consumption. Extending battery life is always a challenge for portable and wearable devices with brighter and larger AMOLED display. Therefore, some of displays have unique power-saving mode, allowing partial output rails in off mode while still retaining information on screen. This can minimize power consumption and maximize battery life.

Richtek’s AMOLED power solutions are designed to optimise performance under specific application requirements. Based on different scenarios, the operating mode will be adjusted to optimise efficiency and delivery best picture quality. Below shows the efficiency performance of the RT4730 for wearable devices over different load current.

the efficiency performance of the RT4730 for wearable devices

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.

The efficiency under different load current

The diagram is the efficiency performance of the Boost converter under different load current with a 3.7V input and a 7V output. Even under the light load condition of 10mA, the efficiency still can reach 91%. This successfully extends battery life. In terms of load regulation as shown below, the portable power solution also has high performance.

the portable power solution

The output voltage only varies ±2 mV over a full load range from 0 to 320 mA from a 3.7V input, which fully meets the requirements of portable applications. Regarding the line regulation as shown below, the output voltage varies only within 1mV when the input voltage changes between 2.8V and 4.7V at 100mA load current. This shows the output voltage is very stable over any input changes, ideal for applications with RF system or in a wide range of supply voltage. The display will remain high performance at any system load/line changes.

high performance at any system load/line changes