AAT3340_08 Datasheet, PDF (8/14 Pages) Advanced Analogic Technologies – High Efficiency 1x/1.5x Charge Pump

ChargePump^TM
Functional Block Diagram
IN
C1+
C1-
Dual-mode
Charge Pump
C2+
1X/1.5X
C2-
4
EN/SET
32-step S²Cwire
Backlight Control
PRODUCT DATASHEET
AAT3340
High Efficiency 1x/1.5x Charge Pump
Control
Logic
OUT
BL1
BL2
BL3
BL4
GND
Functional Description
The AAT3340 is a high efficiency charge pump white LED
driver for portable applications. It can drive 4 white
LEDs.
The AAT3340 is a fractional charge pump and can multiply
the input voltage by 1 or 1.5 times. The charge pump
switches at a fixed frequency of 1MHz. The internal-mode-
selection-circuit automatically switches the mode between
1x and 1.5x mode base on the input voltage, output volt-
age and load current. This mode switching maximizes the
efficiency throughout the entire load range.
When the input voltage is high enough, the AAT3340
operates in 1x mode to provide maximum efficiency. If
the input voltage is too low to supply programmed LED
current, typically when the battery discharges and the
voltage decays, a 1.5x mode is automatically enabled.
When the battery is connected to a charger and the input
voltage become high enough again, the device will
switch back to 1x mode.
The current sink magnitude is controlled by the EN/SET
serial data S²Cwire interface. The interface records rising
edges of the EN/SET pin and decodes them into 32 indi-
vidual current level settings.
Application Information
Current Level Settings
LED current level is set via AnalogicTech’s Simple Serial
Control (S²Cwire) interface in a linear scale where each
code is 0.6mA smaller than the previous code, as shown
in Figure 1. In this manner, the LED current decreases
linearly with each increasing code.
LED Current vs. S²C Data
(V_F = 3.0V @ 20mA)
25
20
15
10
5
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1718 19 20 21 22 23 24 25 26 27 28 29 30 31 32
S²C Code
Figure 1: LED Current Level vs. Simple Serial
Control (S²Cwire).
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3340.2008.07.1.1