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

LP55281

SNVS458B – JUNE 2007 – REVISED JUNE 2007

www.ti.com

Figure 14. Efficiency at Low Load vs Autoload

Functionality of RGB LED Outputs (R1-4, G1-4, B1-4)

LP55281 has 4 sets of RGB/color LED outputs. Each set has 3 outputs, which can be controlled individually with

a 6-bit PWM control register. The pulsed current level for each LED output is set with a single external resistor

Rx_IPLS[7:6] /

Sink Current Pulse

Gx_IPLS[7:6] /

Bx_IPLS[7:6]

00

01

10

11

Rx_PWM[5:0] /

Awerage Sink Current

Pulse Ratio, %

Gx_PWM[5:0] /

Bx_PWM[5:0]

000 000

0

0

000 001

1.6

000 010

3.2

...

...

...

111 110

98.4

111 111

100

Each RGB set must be enabled separately by setting EN_RGBx bit to '1'. Note, that the device must be enabled

(NSTBY = '1') before the RGB outputs can be activated.

When any of EN_RGBx bits are set to '1' and NSTBY = '1', the RGB driver takes a certain quiescent current from

PWM CONTROL TIMING

PWM frequency can be selected from 3 predefined values: 10 kHz, 20 kHz and 40 kHz. The frequency is

selected with FPWM1 and FPWM0 bits, see following table:

FPWM1

FPWM0

0

0

9.92 kHz

14

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