Six-String White LED Driver with Active

Current Balancing for LCD Panel Applications

6

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Typical Operating Characteristics

BOOST CONVERTER EFFICIENCY

vs. INPUT VOLTAGE (BRT = 100%)

INPUT VOLTAGE (V)

94

93

92

91

90

89

88

87

86

712

17

500kHz

750kHz

1MHz

NORMALIZED POWER vs. TOTAL LED CURRENT

(ANALOG AND DPWM DIMMING)

TOTAL LED CURRENT (mA)

1.2

1.0

0.8

0.6

0.4

0.2

0

1

10

100

1000

TOTAL LED

POWER, ANALOG

TOTAL INPUT

POWER, DPWM

TOTAL INPUT

POWER, ANALOG

TOTAL LED

POWER, DPWM

LED CURRENT vs. BRT DUTY CYCLE

(BRT AT 200Hz)

BRT DUTY CYCLE (%)

25

20

15

10

5

0

1

10

100

IDENTICAL FOR DPWM DIMMING

AND ANALOG DIMMING

LED CURRENT

vs. AMBIENT TEMPERATURE (BRT = 100%)

AMBIENT TEMPERATURE (

°)

21.0

20.8

20.6

20.4

20.2

20.0

19.8

19.6

19.4

19.2

19.0

020

60

40

80

LED CURRENT REGULATION

vs. INPUT VOLTAGE

INPUT VOLTAGE (V)

0.05

0.04

0.03

0.02

0.01

0

-0.01

-0.02

-0.03

-0.04

-0.05

712

17

ANALOG DIMMING

BRT = 10%

DPWM DIMMING

BRT = 100%

DPWM DIMMING

BRT = 10%

FB_ VOLTAGE vs. LED CURRENT

(ANALOG DIMMING)

LED STRING CURRENT (mA)

0.7

0.6

0.5

0.4

0.3

0.2

0.1

0

0

5

10

15

20

25

30

SUPPLY CURRENT vs. INPUT VOLTAGE

(DPWM DIMMING)

INPUT VOLTAGE (V)

7

6

5

4

3

2

1

0

712

17

BRT = 100%

BRT = 0%

SHUTDOWN CURRENT vs. INPUT VOLTAGE

INPUT VOLTAGE (V)

7

6

5

4

3

2

1

0

712

17

SWITCHING WAVEFORMS

(BRT = 100%)

MAX8790 toc09

200ns/div

500mA/div

0mA

10V/div

0V