Six-String White LED Driver with Active
Current Balancing for LCD Panel Applications
Typical Operating Characteristics (continued)
(Circuit configuration 1, VIN = 12V, VSHDN = VIN, LEDs = 8 series x 6 parallel strings, ISET = VCC, TA = +25°C, unless otherwise noted.)
SWITCHING WAVEFORMS
(BRT = 15%, ANALOG DIMMING)
MAX8790 toc10
1μs/div
VLX
10V/div
0V
IL
500mA/div
0mA
STARTUP WAVEFORMS
(BRT = 100%, DPWM DIMMING)
MAX8790 toc11
SHDN
5V/div
0V
LED CURRENT WAVEFORMS
(BRT = 50% AT 200Hz, DPWM DIMMING)
MAX8790 toc12
0V
BRT
5V/div
VOUT
0V 20V/div
VFB1
0V 5V/div
VCCV
0V 2V/div
IL
0A 1A/div
ILED
0mA 100mA/div
IL
0A 1A/div
4ms/div
2ms/div
LED CURRENT WAVEFORMS
(BRT = 1% AT 200Hz, DPWM DIMMING)
MAX8790 toc13
0V
BRT
5V/div
VFB1
0V 5V/div
ILED
0mA 100mA/div
IL
0A 1A/div
1ms/div
LED CURRENT WAVEFORMS
(BRT = 50% AT 200Hz, ANALOG DIMMING)
MAX8790 toc14
0V
BRT
5V/div
VFB1
0V 1V/div
ILED
0mA 50mA/div
IL
0A 1A/div
1ms/div
LED CURRENT WAVEFORMS
(BRT = 1% AT 200Hz, ANALOG DIMMING)
MAX8790 toc15
0V
BRT
5V/div
VFB1
0V 2V/div
ILED
0mA 50mA/div
IL
0mA 500mA/div
1ms/div
LED-OPEN FAULT PROTECTION
(BRT = 100%, LED OPEN ON FB3)
MAX8790 toc16
0V
VFB3
1V/div
VFB1
0V 10V/div
VOUT
0V 20V/div
IL
0A 1A/div
20ms/div
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