FUNCTIONAL DEVICE OPERATION
LIGHTING SYSTEM
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
LEDx Current Level (mA)
LEDx[2:0](78)
LEDxHI = 0
LEDxHI = 1
000
001
010
011
100
101
110
111
0
3
0
6
6
12
18
24
30
36
42
9
12
15
18
21
Notes
78. “x“ Represents MD, AD and KP
Table 105. Backlight Drivers Duty Cycle Programming
LEDxDC[5:0](79)
Duty Cycle
000000
0/32, Off
000001
1/32
…
…
010000
16/32
…
…
31/32
011111
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.
13892
Analog Integrated Circuit Device Data
114
Freescale Semiconductor
FREESCALE [ Freescale ]
