LP3958 Datasheet, PDF (16/28 Pages) National Semiconductor (TI) – Lighting Management Unit with High Voltage Boost Converter

Backlight Drivers (Continued)
FADE IN / FADE OUT
LP3958 has an automatic fade in and out for main and sub
backlight. The fade function is enabled with EN_FADE bit.
The slope of the fade curve is set by the SLOPE bit. Fade
control for main and sub display is set by FADE_SEL bit.
Recommended fading sequence:
1. ASSUMPTION: Current WLED value in register
2. Set SLOPE
3. Set FADE_SEL
4. Set EN_FADE = 1
5. Set target WLED value
6. Fading will be done either within 0.65s or 1.3s based on
SLOPE selection
Fading times apply to full scale change i.e. from 0 to 100% or
vice versa. If the current change does not correspond to full
scale change, the time will be respectively shorter. See
WLED Dimming diagrams for typical fade times.
WLED CONTROL REGISTER (03H)
Name Bit
Description
SLOPE 5 FADE execution time:
0 = 1.3s (full scale)
1 = 0.65s (full scale)
FADE_SEL 4 FADE selection:
0 = FADE controls MAIN
1 = FADE controls SUB
EN_FADE 3 FADE enable
0 = FADE disabled
1 = FADE enabled
DISPL
2 Display mode:
0 = MAIN and SUB individual control
1 = MAIN and SUB controlled with
MAIN DAC
EN_MAIN 1 MAIN enable:
0 = disable
1 = enable
EN_SUB 0 SUB enable:
0 = disable
1 = enable
Note: if DISPL=1 and FADE_SEL=0 then FADE effects MAIN and SUB
Adjustment is made with 04H (main current) and with 05H
(sub current) registers:
MAIN CURRENT [7:0]
SUB CURRENT [7:0]
0000 0000
0000 0001
0000 0010
0000 0011
…
…
1111 1101
1111 1110
1111 1111
Driver current,
mA (typical)
0
0.1
0.2
0.3
…
…
25.3
25.4
25.5
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