3. TECHNICAL BRIEF
LG Electronics 40/115 LGE Property
3.10 LCD back-light illumination
Figure 12 LCD Back light charge pump IC
The AAT3369 is a high efficiency charge pump white LED driver for portable applications. It can drive 6 white
LEDs. The current sink magnitude is controlled by either the EN/SET serial data S
2Cwire interface.
The interface records rising edges of the EN/SET pin and decodes them into 32 individual current level
settings. Code 1 is full scale (31mA), and Code 32 is 0.5mA. The modulo 32 interface wraps states back to
state 1 after the 32nd clock. The counter can be clocked at speeds up to 1MHz, so intermediate states are not
visible. The first rising edge of EN/SET enables the IC and initially sets the output LED current to full scale, the
lowest setting equal to 0.5mA. Once the final clock cycle is input for the desired brightness level, the EN/SET
pin should be held high to maintain the device output current at the programmed level. The device is
disabled 500μs after the EN/SET and PWM pin enters a logic low state. The EN/SET timing is designed to
accommodate a wide range of data rates. After the first rising edge of EN/SET, the charge pump is enabled
and reaches full capacity after the soft-start time (T
SS). Exact counts of clock pulses for the desired current
level should be entered on the EN/SET pin with a single burst of clocks.
The counter refreshes each time when a new burst clock input to the EN/SET pin is detected. A constant
current is sunk as long as EN/SET remains in a logic high state. The current sink pins are switched off after
EN/SET and PWM has remained low state for at least the t
OFF timeout period (see Figure 1).
Figure 13 S2C wire Timing Diagram
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