A solution to activate the phone LEDs while maintaining low standby power consumption

As users' demands for mobile phone functions are growing, a new demand has entered the consideration of mobile phone manufacturers, that is, mobile phones can provide LED prompts to provide status, so as to remind users to pay attention to unread messages while on standby. Arrival appointment arrangements or other notices. Several recently released phones have even been badly rated because they did not provide LED prompts. At the same time, users want the phone's standby time to be longer. These two seemingly simple problems have caused handset manufacturers to fall into an unexpected dilemma: how to maintain low total standby power while powering LEDs?

LED indicators are typically powered by a power management IC (PMIC) or other small processor. This is fine when the phone is awake, but the processor must continue to master the timing, even if it is in sleep mode, automatically enable and disable each LED. To achieve this, a few milliamps of standby current is added when powering up the entire PMIC. The data and calculation examples in Table 1 show that the average power consumption is primarily determined by the quiescent current during the LED's extinction.

The LED driver ADP8866 is uniquely designed to meet this challenge. It can easily perform autonomous lighting on four LEDs, and the LEDs can be turned off from 100 ms to 25.2 s. When the autonomous lighting program is executed and these LEDs are off, the total IC current drops below 300 μA. In addition, since all timings are controlled by the ADP8866, these LEDs remain fully synchronized, even in complex or long-lasting flash modes. The following two examples are used to illustrate.

Example 1: Color LED indicator

The phone requires 7 LEDs for backlight display and two LEDs for indication. Due to cost and mechanical requirements, handset manufacturers use red/green (RG) LEDs to effectively implement standby notifications for three conditions: unread messages, low battery levels, and appointment schedules. For each condition, the LED emits a different color of light: red, green or yellow (red + green).

The ADP8866 provides an ideal solution for this common situation, as shown in Figure 1. It has a total of nine LED channels, seven of which are used to illuminate the display, and the red and green signals of the RG LED are controlled by the remaining two channels, producing the blinking pattern shown in Figure 2.

The evaluation board for the DP8866 includes a graphical programming utility, as shown in Figure 3; its I2C register is set to perform the indicator blinking function.

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Hangzhou Qiantang River Electric Group Co., Ltd.(QRE) , https://www.qretransformer.com