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3. TECHNICAL BRIEF
LED Backlight Current
RT9396 communicates with a host (master) Using the standard I2C 2-wire interface.
The two bus lines of SCL and SDA must be pulled high when the bus is not in use. Internal pull-up
resistors are installed. After the START condition, the I2C master sends a chip address. This address is
eight bits long, consisting of seven address bits and a following data direction bit (R/W). The RT9396
address is 10101000 (A8h) and is a receive-only (slave) device. The second word selects the register to
which the data will be written. The third word contains data to write to the selected register. Figure 2
shows the writing information for the four LDOs as well as for each LED current. In the second word, the
sub-address of the four LDOs is "001" and the sub-address of the LED Driver for different dimming
modes are respectively "010", "011" and "100". For the LDO output voltage setting, bits B1 to B4
represent each LDO channel respectively where a "1" indicates selected and a "0" means not selected.
The B0 bit controls on/off (1/0) mode for the selected LDO channel(s). Then, in the third word, bite C0 to
C3 control a 16-step setting of LDO1 to LDO4.The voltage values are listed in Table 1. For LED dimming,
there are three operating modes (Backlight I, Backlight II and Backlight III) to select from by writing
respectively "010", "011" and "100" into the First three bits of the second word, It should be noticed that
no matter which mode is selected, LED1 to LED3 must be turned on, else LED4 to LED6 can not be
Turned on. When backlight I is selected, all six LEDs have the same behavior. Their 64-step dimming
currents are set by bits C0 to C5, which are listed in Table 2. The bits C6 and C7 determine the fade in/out
time of each step as shown in Figure 2. For Backlight II and Backlight III, two sets of LEDs, called Main and
Sub, can work separately.
Backlight Quiescent Current
The quiescent current required to operate all four backlights is reduced by 1.5mA when backlight
current is set to 4.0mA or less. This feature results in higher efficiency under light-load conditions.
Further reduction in quiescent current will result from using fewer than four LEDs.
LGE Internal Use Only
3. TECHNICAL BRIEF
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Copyright © 2010 LG Electronics. Inc. All right reserved.
Only for training and service purposes
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