LP3958 Datasheet, PDF (17/36 Pages) National Semiconductor (TI) – Lighting Management Unit with High Voltage Boost Converter

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LP3958
SNVS423C – JANUARY 2006 – REVISED MARCH 2013
V_BOOST
External PWM
en_sub_pwm
sub[7:0]
en_sub
&
8-Bit IDAC
SUB
Figure 17. SUB output for 2 LEDs (DISPL = 0)
VBOOST
VBOOST
External PWM
en_main_pwm
main[7:0]
en_main
&
8-Bit IDAC
MAIN
Figure 18. MAIN and SUB outputs for 8 LEDs (DISPL = 1)
PWM CONTROL
External PWM control is enabled by writing 1 to EN_MAIN_PWM and/or EN_SUB_PWM bits in register address
2BH. GPIO[0] pin is used as external PWM input when EN_PWM_PIN is set high. PWM input is active high, i.e.
LED is activated when in high state.
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
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