LP5891 datasheet(16/74 Pages) TI

16 / 74 page

The maximum output current per channel, IOUTSET, is determined by resistor RIREF, and the GAINBC. The voltage

on IREF is typically 0.8 V. RIREF can be calculated by Equation 1 below. For noise immunity purpose, suggest

RIREF < 40 kΩ.

+4'(

(G×) =

+4'(

(8)

+4'(

(I#)

+4'(

(8)

1765'6

(I#)

× )#+0($%)

(1)

7.3.2.2 Color Brightness Control (CC) Function

The LP5891 device is able to adjust the output current of each of the three color groups R0-R15, G0-G15, and

B0-B15 separately. This function is called color brightness control (CC). For each color, it has 8-bit data register,

CC_R, CC_G, or CC_B. Thus, all color group output currents can be adjusted in 256 steps from 0% to 100%

of the maximum output current, IOUTSET. The output current of each color, IOUT_R (or G or B) can be calculated by

Equation 2 below.

176

_4(KN ) KN $) =

1765'6

1 + %%_4(KN %%_) KN %%_$)

256

(2)

Table Table 7-3 shows the CC data versus the constant-current against IOUTSET:

Table 7-3. CC Data vs Current Ratio

CC Register (CC_R or CC_G or

CC_B)

Ratio of IOUTSET

0000 0000b

1/256

0.39%

0000 0001b

2/256

0.78%

...

0111 1111b (default)

128/256

50%

...

1111 1110b

255/256

99.61%

1111 1111b

256/256

100%

7.3.2.3 Choosing BC/CC for a Different Application

BC is mainly used for global brightness adjustment to adapt to ambient brightness, such as between day and

night, indoor and outdoor.

• Suggested BC is 3h or 4h, which is in the middle of the range, allowing flexible changes in brightness up and

down.

• If the current of one color group (usually R LEDs) is close to the output maximum current (10 mA or 20

mA), to prevent the constant output current from exceeding the upper limit in case a larger BC code is input

accidentally, choose the maximum BC value, 7h.

• If the current of one color group (usually B LEDs) is close to the output minimum current (0.2 mA), to prevent

the constant output current from exceeding the lower limit in case a lower BC code is input accidentally,

choose the minimum BC code, 0h.

CC can be used to fine tune the brightness in 256 steps. This is suitable for white balance adjustment between

RGB color group. To get a pure white color, the general requirement for the luminous intensity ratio of R, G,

B LED is 5:3:2. Depending on the characteristics of the LED (Electro-Optical conversion efficiency), the current

ratio of R, G, B LED is much different from this ratio. Usually, the Red LED needs the largest current. Choose

255d (the maximum value) CC code for the color group that needs the largest initial current, then choose proper

CC code for the other two color groups according to the current ratio requirement of the LED used.

7.3.3 Frequency Multiplier

The LP5891 has an internal frequency multiplier to generate the GCLK by SCLK. The GCLK frequency can be

configured by FREQ_MOD (See FC0 for more details) and FREQ_MUL (see FC0 for more details ) from 40 MHz

to 160 MHz. As Figure 7-6 shows, if the GCLK frequency is not higher than 80 MHz, the GCLK_MOD is set

LP5891

SLDS269A – MARCH 2022 – REVISED MAY 2022

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