In wearable applications, the AMOLED display size is small, such as 1 -2 inches, so the power consumption is low. One of challenges for wearable designs is the PCB board space. Richtek has developed the wearable power solution RT4730, where a single inductor can support multiple outputs for space-constraint AMOLED display designs.

As to portable applications, the AMOLED display size is up to 5.5 inches or more. A different power supply topology is introduced to support higher pixels, voltage, current and brightness. The following diagram shows Richtek’s AMOLED display power solution for mobile phones. It integrates two Boost converters and one inverting DCDC converter to provide two positive voltage rails and one negative voltage rail required by AMOLED display. It delivers more power than RT4730.

The input voltage range of this solution is 2.9V ~ 4.8V to support lithium ion/lithium polymer battery power. The VO1 output voltage is 4.6V ~ 5.0V supporting 320mA output current ; the VO2 output voltage is - 1.4V ~ -5.4V (SET=H) or -0.8V ~ -4.8V (SET=L), supporting 320mA output current; the VO3 output voltage is 6.8V ~ 7.8V, supporting 150mA output current.

The EN is the enable control of VO3, and the CTRL is the enable control of both VO1 and VO2. The CTRL is also programmed by SWIRE pulses for voltage adjustment of VO1, VO2 and VO3, switch mode control, slew rate and more.

This power solution is housed in a CSP or a QFN package to optimise small space designs. It operates at a fixed operating frequency in PWM mode, also supporting the energy-saving operation mode. Featuring excellent transient response, adjustable output voltage levels, and high efficiency, it is ideal for AMOLED portable devices.