LP85571 datasheet(33/49 Pages) TI2

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LP8557, LP85571

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SNVSA15B – DECEMBER 2013 – REVISED DECEMBER 2015

9.1.2.1 Setting Boost Switching Frequency

The LP8557I boost converter switching frequency is set to 500 kHz by default. It may be re-programmed by

overriding the BFREQ bit with an I2C write. Table 5 shows the boost switching frequency options available.

Table 5. Available Boost Switching Frequencies

BFREQ

ƒSW [kHz]

500

1000

9.1.2.2 Setting Boost Compensation

For stable LP8557I boost operation, appropriate boost compensation must be selected based on the selected

boost switching frequency and the boost inductance. Table 6 shows recommended boost compensation options

based on the boost switching frequency and selected boost circuit inductance.

Table 6. Recommended Boost Compensation Options Based

on the Boost Switching Frequency and Inductance

RECOMMENDED BOOST

ƒSW (kHz)

L (µH)

COMPENSATION OPTION

500

4.7

1000

6.8

The LP8557I boost converter compensation is set to option 1 by default. It may be re-programmed by overriding

the BCOMP bit with an I2C write. Table 7 shows available boost compensation options.

Table 7. Available Boost Compensation Options

BCOMP

BOOST COMPENSATION

OPTION

9.1.2.3 Setting PWM Dimming Frequency

The LP8557I PWM dimming frequency is set to 9.8 kHz by default. It may be re-programmed by overriding the

PFREQ bits with an I2C write. Table 8 summarizes available PWM dimming frequencies.

Table 8. Available PWM Dimming Frequencies

PFREQ

ƒPWM (kHz)

000

4.9

001

9.8

010

14.6

011

19.5

100

24.4

101

29.3

110

34.2

111

39.1

9.1.2.4 Setting Full-Scale LED Current

The LP8557I full-scale LED current is set to 25 mA by default. It may be re-programmed by overriding

MAXCURR bits with an I2C write. Table 9 shows available full-scale LED current levels.

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