13892 datasheet(114/156 Pages) FREESCALE

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Analog Integrated Circuit Device Data

114

Freescale Semiconductor

13892

FUNCTIONAL DEVICE OPERATION

LIGHTING SYSTEM

The lighting system includes backlight drivers for main display, auxiliary display, and keypad. The backlight LEDs are

configured in series. Three additional drivers are provided for RGB or general purpose signaling.

BACKLIGHT DRIVERS

The backlight drivers LEDMD, LEDAD and LEDKP are independent current sink channels. Each driver channel features

programmable current levels via LEDx[2:0] as well as programmable PWM duty cycle settings with LEDxDC[5:0]. By a

combination of level and PWM settings, the backlight intensity can be adjusted, or a soft start and dimming feature can be

implemented. The on period of the serial LED backlight drivers will be adapted to take into account that the serial LED switcher

startup time is longer than one half the minimum of the period of the backlight drivers.

When applying a duty cycle of less than 100% the backlight drivers will be turned on and off at a repetition rate high enough

to avoid flickering and or beat frequencies with the different types of displays. Also, to avoid high frequency spur coupling in the

application, the switching edges of the output drivers are softened.

The current level is programmable in a low range mode and in a high range mode through the LEDxHI bit. This facilitates the

current setting, in case two or more serial LED strings are connected in parallel to the same driver or when using super bright

LEDs.

Table 104. Backlight Drivers Current Programming

000

001

010

011

100

101

110

111

Notes

78.

“x“ Represents MD, AD and KP

Table 105. Backlight Drivers Duty Cycle Programming

000000

0/32, Off

000001

1/32

…

010000

16/32

…

011111

31/32

100000 to 111111

32/32, Continuously On

Notes

79.

“x” represents MD, AD, or KP

Ramp up and ramp down patterns are implemented in hardware to reduce the burden of real time software control via the SPI

to orchestrate dimming and soft start lighting effects. Ramp patterns for each of the drivers is accessed with the corresponding

LEDxRAMP bit.

LEDx[2:0](78)

LEDx Current Level (mA)

LEDxHI = 0

LEDxHI = 1

LEDxDC[5:0](79)

Duty Cycle

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