LP85571 datasheet(31/49 Pages) TI2

31 / 49 page

LP8557, LP85571

www.ti.com

SNVSA15B – DECEMBER 2013 – REVISED DECEMBER 2015

9 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

9.1 Application Information

9.1.1 Designing With LP8557

The LP8557 is intended for applications without an I2C master. It can be fully controlled with an external PWM

signal. Boost switching frequency, boost compensation, PWM dimming frequency, and the maximum LED

current can be set with external resistors.

9.1.1.1 Setting Boost Switching and PWM Dimming Frequencies

Boost switching frequency and PWM dimming frequency are set by connecting a resistor from the FSET pin to

GND. Available options are shown in Table 2.

Table 2. Setting Boost Switching and PWM Dimming Frequencies With an

External Resistor

RFSET [

Ω] (TOLERANCE)

ƒSW (kHz)

ƒPWM (kHz)

470k - 1M (±5%)

500

4.9

300k, 330k (±5%)

500

9.8

200k (±5%)

500

14.6

147k, 150k, 154k, 158k (±1%)

500

19.5

121k (±1%)

500

24.4

100k (±1%)

500

29.3

86.6k (±1%)

500

34.2

75.0k (±1%)

500

39.1

63.4k (±1%)

1000

4.9

52.3k, 53.6k (±1%)

1000

9.8

44.2k, 45.3k (±1%)

1000

14.6

39.2k (±1%)

1000

19.5

34.0k (±1%)

1000

24.4

30.1k (±1%)

1000

29.3

26.1k (±1%)

1000

34.2

23.2k (±1%)

1000

39.1

0 (grounded)

500

9.8

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