AAT2842 Datasheet, PDF (13/21 Pages) Advanced Analogic Technologies – High-Current Charge Pump with S2Cwire™ Control and Dual LDO for Backlight and Flash

AAT2842
High-Current Charge Pump with S²Cwire™
Control and Dual LDO for Backlight and Flash
R2 Standard 1% Values (R1 = 120K)
V_OUT (V)
R2 (Ω)
2.8
160K
2.5
130K
2.0
79.6K
1.8
60.4K
1.5
30.1K
Table 3: Example Output Voltages and
Corresponding Resistor Values.
Altering the Maximum LED Current
Level from 30/150mA
The value of R_BSET determines the maximum LED
current level for the backlight section. In the typical
application, selecting R_BSET = 280kΩ results in
30mA/channel LED current. From this reference
point, the maximum current level can be modified
by calculating an alternative R_BSET value:
30mA · 280kΩ
R_BSET =
I_LED(MAX)
This is illustrated graphically in Figure 3.
Maximum Backlight LED Current vs. R_BSET
45
40
35
30
25
20
15
10
5
0
100 200 300 400 500 600 700 800 900 1000 1100
R_BSET (kΩ)
Figure 3: Maximum LED Current vs R_BSET.
Similarly, the value of R_FSET determines the maxi-
mum LED current level for the flash section. In the
typical application, selecting R_FSET = 280kΩ results
in 150mA/channel LED current. From this refer-
ence point, the maximum current level can be mod-
ified by calculating an alternative R_FSET value:
150mA · 280kΩ
R_FSET =
I_FLED(MAX)
This is illustrated graphically in Figure 4.
Maximum Flash LED Current vs. R_FSET
240
220
200
180
160
140
120
100
80
60
40
20
0
100 200 300 400 500 600 700 800 900 1000 1100
R_FSET (kΩ)
Figure 4: Maximum LED Current vs. R_FSET.
Selection of set resistor values outside of the typi-
cal application must be carefully evaluated to
ensure that the application's performance require-
ments can still be met.
Brightness Control Using the BSET and
FSET Pins
An alternative method can be used for brightness
control of the flash and/or backlight sections by uti-
lizing the corresponding set resistor pin. By using a
digital I/O port or DAC output, an alternative bright-
ness control technique can be created for each
lighting section, as shown in Figure 5.
HI/LO
or
V_DAC
R2
R₁
AAT2842
SET
Figure 5: Brightness Control Using Either SET
Resistor Pin.
2842.2006.10.1.0
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