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How to activate the phone LED indicator is not affected while maintaining standby time

In Electronic Infomation Category: H | on April 28,2011

With the functional requirements of mobile users growing, the demand for a new mobile phone manufacturer into consideration, the phone can be prompted to provide state of the LED in order to standby at the same time, alerts you have unread messages , upcoming appointments or other arrangements for notification. Recently released several mobile phone because there is no provision of even been worse * LED prompts. At the same time, users want the standby time can be longer. These two seemingly simple questions so that handset manufacturers into an unexpected dilemma: how to prompt for the LED power supply while maintaining a low total standby power consumption?

LED lights usually power management IC (PMIC) or other small processor power. When the phone is awake, this is no problem, but the processor must continue to master the timing, even in sleep mode, but also automatically enable and AS1581T datasheet and disable the LED. To achieve this functionality, the power for the entire PMIC will increase the number of mA of standby current. Table 1 shows examples of data and AS1581T price and calculations, the average power consumption during the light goes out mainly by the static current decision.

Table 1. Flash mode (7.5 s off / 300 ms on) under the current and AS1581T suppliers and power (10mA LED current and 3.7 V input)

Power Management





standard PMIC

5 mA < / P>

15 mA < / P>

5.39 mA < / P>

19.9 mW < / P>

ADP8866 < / o: p>

300 A

11 mA < / P>

710 A

2.6 mW < / P>


0 A

10 mA < / P>

385 A

1.4 mW < / P>

LED driver ADP8866 uses a unique configuration, particularly in response to this challenge, it can easily perform the four LED indicator light independent process, the LEDs off time to 100 ms to 25.2 s in the range set. When the self-lighting program execution and when the LED is off, IC total current is reduced to 300? A below. In addition, since all the timing control by the ADP8866, these LED still maintain full synchronization, even in complex or long duration flash mode. The following two examples to illustrate.

Example 1: Color LED Indicator

Phone needs seven LED for the backlight display, two LED for indication. Due to cost and mechanical requirements, handset manufacturers use Red / Green (RG) LED to the effective realization of the three conditions of standby notice: unread messages, low battery and dating arrangements. For each state, LED emits light in different colors: red, green or yellow (red + green). This common scenario for

ADP8866 provides an ideal solution shown in Figure 1. It is a total of nine LED channels, which used to illuminate the display 7, RG LEDs red and green signals from the control of the remaining two channels, resulting in flash mode as shown in Figure 2.

Figure 1. ADP8866 lighting and LED indicator backlight control settings

ADP8866s * The evaluation board includes a graphical programming utility, shown in Figure 3; the I2C register set to perform light is flashing function.

Register settings shown in Figure 3 will produce the first 250 ms of 10 mA a red light (Sink 8) pulse, until extinguished 500 ms after the red light to generate a 250 ms pulse. The second red light pulse and green mix to produce yellow light pulse, so only half the current consumption (5 mA), can provide the same brightness. Green LED (Sink 9) has a similar setup, but the first pulse will be delayed. When the second green light pulse goes out, the system will wait 12 seconds, then repeat. Enable this sequence, all three colors are successively repeated flashes, shown in Figure 2. If you want red or green light, only enable the first or third pulse. If you only need to produce red and yellow, then a red LED to be in the first and second pulse is enabled, the green LED should only be enabled in the second pulse.

Figure 2. Red and green flash pulse sequence and the resulting color

Figure 3. ADP8866 LED indicator for programming graphical user interface

Popular green light overlap, the current decreases, so the brightness of all three the same color light. You can also change the current red and green to produce the RG spectrum of other colors. Pulse width, closing time and amplitude is completely customizable, so a wide variety of lighting effects are possible.

Example 2: Dynamic light is highly visible

Portable electronic devices require notice the dynamic nature of light and high visibility to the background interference in other conspicuously apparent. In this regard, ADP8866 is also an ideal solution, it can be used up to 4 LED channels (Sink 6 to Sink 9) to drive the complex lighting sequences. The remaining five LED channel can be used to backlight or keypad lighting. In this case, Sink 6 to Sink 9 is set to light up four LED, first from right to left, from left to right, after a delay of 10 seconds and then repeat. The model shown in Figure 4.

Figure 4. Four-channel dynamic light show

Fade time, fade time and gradient settings (square or cube) while for the first HB (heartbeat) pulse and setting. DELAY parameter can range from 0 to 1.270 seconds, within 10 ms increments to adjust. In this case, DELAY is set to gradually bright half the time, but you can use other delay settings for different effects. The first pulse and the off time between pulses HB by the first pulse OFF Time (closing time) variable control. To maintain symmetry, these times are set to a multiple of the delay time. HB OFF Time to set the delay before the sequence repeats. In this case, the waiting time of 10 seconds, Sink 6 HB OFF Time to 10 seconds. The other three HB OFF Time DELAY time is equal to 10 seconds plus a multiple of. Register state corresponding to the sequence shown in Figure 5.

Figure 5. ADP8866 light programming for dynamic graphical user interface

Can also use the same programming methods to generate interesting flashing lights, cell phone ring tones, notifications, and other modes. Automatic dimming feature gradually light and light can enhance the visual appeal, but the extra time will result in gradual increase in average power consumption slightly. Any case, when all the LED are extinguished, ADP8866 will automatically go back to sleep, wake up in time when necessary, to start the next LED sequence.

ADP8866 backlight LED charge pump driver sets and automatic flash functions in one, support for nine independently programmable LED drive, maximum power consumption of 25 mA. Current level, gradient time and a flash rate can be independently programmed and implemented, can set the backlight LED light and fades gradually independent of time. With 2.5 V to 5.5 V power supply, dual-capacitor charge pump provides up to 240 mA of current. Design also integrated soft-start, short circuit protection, overvoltage and overtemperature protection, and therefore stable and reliable. Samples in 20-pin 4-mm 4-mm LFCSP (QFN) package and also provide the * evaluation board, graphics programming procedures and technical documentation.

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