As shown in the diagram, AVDD is generally set at 3.3V, for the drive circuit of AMOLED displays; OVDD is pre-set at 3.3V, ranging from 2.8V to 4.2V in 100mV per step for the positive voltage rail; OVSS is pre-set at -3.3V, ranging from -0.6V to -4V in 100mV per step for the negative voltage rail.
To ensure the accuracy of each output rail as well as fast transient response, linear regulators (LDOs) are usually used as the final power stage. The charge pump circuit operating in switch mode converts the positive voltage to a negative voltage. The Buck-Boost circuit converts the input battery voltage to intermediate voltage rails which are normally set higher than the maximum value of AVDD, OVDD or -OVSS by 0.2V. Therefore, regulators in the next stage have enough head room for adjustment to achieve better efficiency and performance.
The RT4730 application circuit only uses one inductor for three adjustable output rails. All output voltage rails can be adjusted by SWIRE interface protocols, allowing users to switch on/off each output rail and to programme voltage levels via SWIRE pulses.
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