LP8550TLESLASHNOPB datasheet(17/49 Pages) TI1

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+1 LSB

PWM value 510 (10-bit)

PWM value 510 1/2 (10-bit)

PWM value 511 (10-bit)

Brightness (PWM)

Time

Slope Time

Advanced slope

Brightness (PWM)

Sloper Input

PWM Output

Time

Normal slope

Steady state without dithering

If dither is enabled it will

be used during transition

to enable smooth effect

LP8550

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SNVS657E – SEPTEMBER 2010 – REVISED SEPTEMBER 2014

8.3.2.15 Slope and Dithering

During transition between two brightness (PWM) values special dithering scheme is used if the slope is enabled.

It allows increased resolution and smaller average steps size. Dithering is not used in steady state condition.

Slope time can be programmed with EEPROM bits <SLOPE[3:0]> from 0 to 500 ms. Same slope time is used for

sloping up and down. Advanced slope makes brightness changes smooth for eye. Dithering can be programmed

with EEPROM bits <DITHER[1:0]> from 0 to 3 bits. Figure 16 below is for 1-bit dithering; for 3-bit dithering, every

8th pulse is made 1 LSB longer to increase the average value by 1/8 of LSB.

Figure 15. Sloper Operation

Figure 16. Example Of The Dithering,

1-Bit Dither, 10-Bit Resolution

8.3.2.16 Driver Headroom Control

Driver headroom can be controlled with <DRV_HEADR[2:0]> EEPROM bits. Driver headroom control sets the

minimum threshold for the voltage over the LED output which has the smallest driver headroom and controls the

boost output voltage accordingly. Boost output voltage step size is 125 mV. The LED output which has the

smallest forward voltage is the one which has highest VF across the LEDs. The strings with highest forward

voltage is detected automatically. To achieve best possible efficiency smallest possible headroom voltage should

be selected. If there is high variation between LED strings, the headroom can be raised slightly to prevent any

visual artifacts.

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