LG -T370 Service Manual page 49

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 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 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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3. TECHNICAL BRIEF
Only for training and service purposes