RT4539A

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DS4539A-01

December 2022

22

Advanced Brightness Control

Dimming control is received either from PWM input pin or from I2C interface. Through I2C interface, both of 0x04h

and 0x05h are used to control brightness. Moreover, the 8-bits in address 0x05h register (LSB) along the 4-bits

defined in address 0x04h register (MSB) allow LED brightness to be set in 12-bit fine steps.

More setting details are shown in Table 9.

Table 9. Advanced Brightness Control

Address Bit

Name

Default Value

Description

R/W

07h

[1:

0]

Advanced

Brightness Control

External PWM

signal

(B00)

B00: External PWM signal

B01: I2C brightness register (04h, 05h)

B10: External PWM signal multiplied with I2C

brightness register (04h, 05h)

R/W

The dimming mode can be programmed by address 0x00h register but the exponential function is valid for DC mode

only. If users select PWM mode, the PWM and/or I2C interface will directly control the LED current. In the following

section, we will describe how to set address 0x07h by DC mode only.

LED Current with Advanced Brightness Control Selection “00”

LED brightness mapping can be selected to be either linear or exponential (DC mode only) by address 0x03h [7].

When address 0x07h is set to B00 and exponential mode is selected by address 0x03h, the PWM duty will transfer

cycle-to-current response with 11-bit resolution and target ILED is approximated by the following equation:

ILED=50μA×1.00304 2047×PWM duty

(forPWMduty≠0)@ILEDmax=25mA

It is valid for PWM duty cycles within 0~100%. If duty cycle is 0, the brightness will be disabled.

When address 0x07h is set to B00 and linear mode is selected by address 0x03h, the PWM duty will transfer

cycle-to-current response with 12-bit resolution and target ILED is approximated by the following equation :

ILED=6.105uA×4095×PWM duty

(forPWMduty≥0) @ILEDmax=25mA

It is valid for PWM duty cycles within 0~100%. If duty cycle is 0, the brightness will be disabled.

Slope Time

ILED_t1

ILED_t0

t1

t0

1. At time t0, the PWM duty cycle changes from 40% to 80%

2. Mapping mode is set to linear with DC mode

3. ILED_t0=25mA x 40%=10mA

4. ILED_t1=25mA x 80%=20mA

Figure 6.

LED Current with Advanced Brightness Control Selection “01”

LED brightness mapping can be selected to be either linear or exponential (DC mode only) by address 0x03h [7].

When address 0x07h is set to B01 and exponential mode is selected by address 0x03h, the I2C interface will

transfer code-to-current response with 11-bit resolution and target ILED is approximated by the following equation :

ILED = 50uA×1.00304I

2C code

(forcodes>0) @ILEDmax=25mA