AAT2806 datasheet(11/16 Pages) AAT

11 / 16 page

The flash charge pump is a charge pump doubler

with regulated output voltage. It is designed to deliv-

er 120mA of continuous current and 250mA of pulsed

current.

The AAT2806 requires six external components:

three 1µF ceramic capacitors for the charge pump

flying capacitors (C1, C2, and C3), one 1µF ceram-

ic input capacitor (CIN), one 0.33µF to 1µF ceramic

capacitor for the backlight charge pump output

capacitor (COUT), and one 1µF ceramic capacitor

for the flash charge pump output capacitor (COUT).

Constant Current Output Level Settings

The constant current level for the LED channels is set

via the S2Cwire serial interface (see Table 1).

Because the inputs D1 to D4 are true independent

constant current sinks, the voltage observed on any

single given input will be determined by the differ-

ence between VOUT and the actual forward voltage

(VF) of the LED being driven.

Since the constant current levels are programma-

ble, no PWM (pulse width modulation) or addition-

al control circuitry is needed to control LED bright-

ness. This feature greatly reduces the burden on a

microcontroller or system IC to manage LED or dis-

play brightness, allowing the user to "set it and for-

get it." With its high-speed serial interface (>1MHz

data rate), the LED current drive can be changed

successively to brighten or dim LEDs, in smooth

transitions (e.g., to fade-out) or in abrupt steps, giv-

ing the user complete programmability and real-

time control of LED brightness.

The AAT2806 offers an additional Low Current mode

with reduced quiescent current (Data 13 to 16). This

mode is especially useful for low-current applications

where a continuous, low-current state is maintained.

The reduction in quiescent current significantly

reduces the impact due to maintaining a continuous

backlighting state.

Table 1: Constant Current Programming Levels.

S2Cwire Serial Interface

The current sink input magnitude on the backlight

charge pump is controlled by AnalogicTech's

S2Cwire serial digital input. The interface relies on

the number of rising edges of the EN/SET pin to

address and load the registers. S2Cwire latches

data or address after the EN/SET pin has been

held high for time TLAT. The interface records rising

edges of the EN/SET pin and decodes them into 16

different states, as indicated in Table 1. There are

four brightness levels for the main or sub-display

group with the possibility of individually turning ON

or OFF each group. To further optimize power effi-

ciency, the device also offers four low-current lev-

els for dim LED operation (Data 13 to 16). During

this low-current mode, the internal supply current

reduces to only 50µA typical.

The counter can be clocked at speeds up to 1MHz,

such that intermediate states are not visible. The

first rising edge of EN/SET enables the IC and ini-

tially sets the output LED current to 20mA. Once

the final clock cycle is input for the desired bright-

ness level, the EN/SET pin is held high to maintain

the device output current at the programmed level.

The device is disabled 500µs (TOFF) after the

EN/SET pin transitions to a logic low state.

IOUT (mA)

Data

D1-D3

Sub-Group D4

0.05

0.5

AAT2806

Dual High Efficiency Charge Pump

for White LED and Flash Applications

2806.2006.04.1.8

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