Six-String White LED Driver with Active

Current Balancing for LCD Panel Applications

8

_______________________________________________________________________________________

Typical Operating Characteristics (continued)

LED-SHORT FAULT PROTECTION

(BRT = 100%, 2 LEDs SHORT ON FB3)

10ms/div

0A

1V/div

10V/div

20V/div

1A/div

0V

0V

0V

MAX8790 toc17

LED CURRENT BALANCING

vs. INPUT VOLTAGE (BRT = 100%)

INPUT VOLTAGE (V)

1.00

0.90

0.80

0.70

0.60

0.50

0.40

0.30

0.20

0.10

0

712

17

750kHz

500kHz

1MHz

Pin Description

PIN

NAME

FUNCTION

1

OSC

1MHz. Connect OSC to GND to set the frequency to 500kHz. Float OSC to set the frequency to 750kHz.

2

ENA

Analog Dimming Enable. ENA sets the PWM control mode. Set ENA LOW to enable direct DPWM dimming.

Set ENA HIGH to enable analog dimming. In both modes, the duty cycle of the PWM signal at the BRT input

controls the LED current characteristics. See the Dimming Control section for a complete description.

3

BRT

Brightness Control Input. The duty cycle of this digital input signal controls the LED current characteristics.

The allowable frequency range is 100Hz to 500Hz in analog dimming mode. The duty cycle can be 100%

to 1%. The BRT frequency can go above 500Hz in direct DPWM mode as long as the BRT pulse width is

greater than 50µs minimum. See the Dimming Control section for a complete description.

4

SHDN

Shutdown Control Input. The MAX8790 shuts down when SHDN is less than 0.8V. Pulling SHDN above

2.1V enables the MAX8790. SHDN can be connected to the input voltage if desired.

5

FB1

LED String 1 Cathode Connection. FB1 is the open-drain output of an internal regulator, which controls

current through FB1. FB1 can sink up to 25mA. If unused, connect FB1 to GND.

6

FB2

LED String 2 Cathode Connection. FB2 is the open-drain output of an internal regulator, which controls

current through FB2. FB2 can sink up to 25mA. If unused, connect FB2 to GND.

7

FB3

LED String 3 Cathode Connection. FB3 is the open-drain output of an internal regulator, which controls

current through FB3. FB3 can sink up to 25mA. If unused, connect FB3 to GND.

8

GND

Ground

9

FB4

LED String 4 Cathode Connection. FB4 is the open-drain output of an internal regulator, which controls

current through FB4. FB4 can sink up to 25mA. If unused, connect FB4 to GND.

10

FB5

LED String 5 Cathode Connection. FB5 is the open-drain output of an internal regulator, which controls

current through FB5. FB5 can sink up to 25mA. If unused, connect FB5 to GND.