
Six-String White LED Driver with Active
Current Balancing for LCD Panel Applications
Typical Operating Characteristics (continued)
( Circuit configuration 1, V IN = 12V, V SHDN = V IN , LEDs = 8 series x 6 parallel strings, ISET = V CC , T A = +25°C, unless otherwise noted.)
SWITCHING WAVEFORMS
(BRT = 15%, ANALOG DIMMING)
MAX8790 toc10
STARTUP WAVEFORMS
(BRT = 100%, DPWM DIMMING)
MAX8790 toc11
SHDN
LED CURRENT WAVEFORMS
(BRT = 50% AT 200Hz, DPWM DIMMING)
MAX8790 toc12
BRT
0V
5V/div
0V
5V/div
V LX
10V/div
0V
V OUT
20V/div
0V
V FB1
5V/div
0V
I L
500mA/div
V CCV
0V 2V/div
I L
I LED
0mA 100mA/div
I L
1 μ s/div
0mA
4ms/div
0A
1A/div
2ms/div
0A
1A/div
LED CURRENT WAVEFORMS
(BRT = 1% AT 200Hz, DPWM DIMMING)
MAX8790 toc13
BRT
LED CURRENT WAVEFORMS
(BRT = 50% AT 200Hz, ANALOG DIMMING)
MAX8790 toc14
BRT
0V
0V
5V/div
V FB1
5V/div
0V
0V
5V/div
V FB1
1V/div
I LED
0mA 100mA/div
I L
I LED
0mA 50mA/div
I L
0A
1A/div
0A
1A/div
1ms/div
LED CURRENT WAVEFORMS
(BRT = 1% AT 200Hz, ANALOG DIMMING)
MAX8790 toc15
BRT
1ms/div
LED-OPEN FAULT PROTECTION
(BRT = 100%, LED OPEN ON FB3)
MAX8790 toc16
V FB3
0V
0V
5V/div
V FB1
2V/div
0V
0V
1V/div
V FB1
10V/div
I LED
0mA 50mA/div
I L
V OUT
0V 20V/div
I L
1ms/div
0mA
500mA/div
20ms/div
0A
1A/div
_______________________________________________________________________________________
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