The mobile phone requires 7 LEDs for backlight display and two LEDs for indication. Due to cost and mechanical requirements, mobile phone manufacturers use red / green (RG) LEDs to effectively implement standby notifications in three situations: unread messages, low battery, and appointment scheduling. For each condition, the LED will emit different colors of light: red light, green light or yellow light (red light + green light).
ADP8866 provides an ideal solution for this common situation, as shown in Figure 1. It has a total of 9 LED channels, 7 of which are used to illuminate the display. The red and green signals of the RG LED are controlled by the remaining two channels, resulting in the blinking pattern shown in Figure 2.
Figure 1. ADP8866 control backlighting and LED indicator settings
The ADP8866 evaluation board includes a graphical programming utility, as shown in Figure 3; its I2C register is set to perform the indicator flashing function.
The register setting shown in Figure 3 will first generate a 250 ms 10 mA red light (Sink 8) pulse, and then generate a 250 ms red light pulse after it goes out for 500 ms. The second red light pulse is mixed with the green light pulse to generate yellow light, so it consumes only half the current (5 mA) to provide the same brightness. The green LED (Sink 9) has a similar setting, but its first pulse is delayed. When the second green light pulse goes out, the system will wait for 12 seconds and then repeat. When this sequence is enabled, all three colors will flash repeatedly in succession, as shown in Figure 2. If a red or green indicator is required, only the first or third pulse needs to be enabled. If only red and yellow notifications are required, the red LED should be enabled on the first and second pulses, and the green LED should only be enabled on the second pulse.
Figure 2. Red and green flashing pulse sequences and the resulting colors
Figure 3. ADP8866 graphical user interface for LED indicator programming
When the red and green lights overlap, the current decreases, so the brightness of all three color indicators is the same. In addition, the red and green light currents can also be changed to produce other colors in the RG spectrum. The pulse width, off time and amplitude are fully customizable, so various lighting effects are possible.
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