RT4539A

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DS4539A-01

December 2022

20

ILED

(mA)

0x02h

<7: 0>

ILED

(mA)

0x02h

<7: 0>

ILED

(mA)

0x02h

<7: 0>

ILED

(mA)

0x02h

<7: 0>

ILED

(mA)

0x02h

<7: 0>

31.28

E0

25.52

B0

19.76

80

14.00

50

31.16

DF

25.40

AF

19.64

7F

13.88

4F

31.04

DE

25.28

AE

19.52

7E

13.76

4E

30.92

DD

25.16

AD

19.40

7D

13.64

4D

30.80

DC

25.04

AC

19.28

7C

13.52

4C

30.68

DB

24.92

AB

19.16

7B

13.40

4B

30.56

DA

24.80

AA

19.04

7A

13.28

4A

30.44

D9

24.68

A9

18.92

79

13.16

49

30.32

D8

24.56

A8

18.80

78

13.04

48

30.20

D7

24.44

A7

18.68

77

12.92

47

30.08

D6

24.32

A6

18.56

76

12.80

46

29.96

D5

24.20

A5

18.44

75

12.68

45

29.84

D4

24.08

A4

18.32

74

12.56

44

29.72

D3

23.96

A3

18.20

73

12.44

43

29.60

D2

23.84

A2

18.08

72

12.32

42

29.48

D1

23.72

A1

17.96

71

12.20

41

29.36

D0

23.60

A0

17.84

70

12.08

40

LED Driver Headroom

The LED driver headroom can be set by the I2C interface and more setting details are shown in Table 7.

This adjusts the Minimum headroom selected comparator threshold with address 0x03h and contributes to the error

amplifier, moreover regulates an optimized output voltage for high efficiency.

Table 7. LED Driver Headroom

Address

Bit

Name

Default Value

Description

Resolution

R/W

03h

[6: 5]

LED driver

headroom

400mV

(B00)

LED driver headroom

B00: 400mV

B01: 450mV

B10: 500mV

B11: 600mV

--

R/W

The RT4539A detects all FBx voltage and selects a minimum voltage to EA (Error Amplifier). When the LED driver

headroom command is below B00, the LED driver headroom will be kept at 400mV and VOUT can be boosted to the

highest forward voltage of LED strings. This function can guarantee that the highest of FB pin voltage is 600mV.

Brightness Control by Address 0x03h/0x04h/0x05h Register

The RT4539A equips various methods of brightness control, including Dimming resolution bit selection, ILED

Mapping (Linear or exponential) mode selection and LED brightness setting. The brightness can be controlled using

an external PWM signal or the brightness register accessible by users via an I2C interface or both. 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 8.