LP55281TLSLASHNOPB datasheet(34/42 Pages) TI2

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1.0

7.8

14.6

21.4

28.2

35.0

LOAD CURRENT (mA)

90.0

74.0

58.0

42.0

26.0

10.0

Autoload ON

Autoload OFF

90.0

74.0

58.0

42.0

26.0

10.0

LP55281

SNVS458D – JUNE 2007 – REVISED OCTOBER 2016

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Figure 31. Efficiency at Low Load vs Autoload

8.3 Initialization Set Up Example

The following table gives an example initialization sequence to illustrate the various LED and Boost configuration

options. Not every feature of the LP55281 is configured in this example.

Table 11. Initialization Example

ADDRESS

DATA

COMMENT

60h

00h

RESET

Execute software reset to initialize LP55281

00h

3Fh

RED 1

IPLS = 0 (25% IRGB), PWM = 100%

01h

5Fh

GREEN1

IPLS = 1 (50% IRGB), PWM = 50%

02h

90h

BLUE1

IPLS = 2 (75% IRGB), PWM = 25.4%

03h

C8h

RED 2

IPLS = 3 (100% IRGB), PWM = 12.7%

04h

1Fh

GREEN2

IPLS = 0 (25% IRGB), PWM = 50%

05h

10h

BLUE2

IPLS = 0 (25% IRGB), PWM = 25.4%

06h

07h

RED 3

IPLS = 0 (25% IRGB), PWM = 11.1%

07h

03h

GREEN3

IPLS = 0 (25% IRGB), PWM = 4.8%

08h

01h

BLUE3

IPLS = 0 (25% IRGB), PWM = 1.6%

09h

RED 4

IPLS = 0 (25% IRGB), PWM = 0%

0Ah

GREEN4

IPLS = 0 (25% IRGB), PWM = 0%

0Bh

BLUE4

IPLS = 0 (25% IRGB), PWM = 0%

0Fh

Boost Output

Boost output voltage set to 4.7V

10h

07h

Frequency

Selections

PWM frequency (FPWM[1:0] = 0, 9.92 kHz), Boost SW frequency =

2 MHz

11h

CFh

Enables

NSTBY, EN_BOOST, EN_RGB4, EN_RGB3, EN_RGB2, EN_RGB1

= 1 (exit standby state, enable boost and rgb drivers)

9 Power Supply Recommendations

The LP55281 is designed to operate from an input supply range of 2.7 V to 5.5 V. This input supply must be well

regulated and able to provide the peak current required by the LED configuration without voltage drop under load

transients (enable on/off). The resistance of the input supply rail should be low enough such that the input

current transient does not cause the LP55281 supply voltage to droop more than 5%. Additional bulk decoupling

located close to the input capacitor (CIN) may be required to minimize the impact of the input supply rail

resistance.

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