RT4539A

Copyright © 2022 Richtek Technology Corporation. All rights reserved.

is a registered trademark of Richtek Technology Corporation

DS4539A-01

December 2022

www.richtek.com

21

Table 8. Brightness Register

Address Bit

Name

Default Value

Description

R/W

03h

[2:

0]

Bit Selection

12bit

(B100)

Brightness Control by I2C Register

B000: 8bit (both linear and exponential)

B001: 9bit (both linear and exponential)

B010: 10bit (both linear and exponential)

B011: 11bit (both linear and exponential)

B100: 12bit (Linear only)

R/W

[7]

ILED Mapping

Mode

Linear

(B0)

B0: Linear

B1: Exponential (DC Mode only)

R/W

04h

[3:

0]

ILED Brightness

MSB Register

0%

(0x00h)

If 03h[2: 0] bit selection is 9bit~12bit,

04h & 05h series write is needed and then ILED

brightness changes

R/W

05h

[7:

0]

ILED Brightness

LSB Register

0%

(0x00h)

0x00h: 0%

0xFFh: 100%

R/W

ILED Brightness Exponential Mapping

The RT4539A embeds an advanced exponential transition function during brightness change to make it more

pleasing to a human eye. The exponential calculation follows the equation below and the and resolution is up to 11

bits.

ILED=ILEDmin×K BRT Code

(forcodes>0&Code0disablesthebacklight)

Where K=1.00304

The exponential function uses different input signal types to calculate target ILED and can be programmed with

advanced brightness control register. More setting details are shown in Table 12.

The exponential function is valid for DC mode only and an example is described in the following Figure.

)

1

( +

D

LED

I

)

(D

LED

I

K

I

I

D

LED

D

LED

×

=

+

)

(

)

1

(

Bit

ILEDmin ILEDmax

K

11

20uA

10mA

1.00304

11

50uA

25mA

11

70uA

35mA

Figure 5