AAT2848 Datasheet, PDF (10/19 Pages) Advanced Analogic Technologies – High-Current Charge Pump For Backlight Display and Flash Applications

ChargePump^TM
PRODUCT DATASHEET
AAT2848
High-Current Charge Pump For Backlight Display and Flash Applications
The two constant flash current sink outputs (FL1 and
FL2) can drive up to two LEDs with a maximum current
of 300mA each. Because the outputs FL1 and FL2 are
true independent constant flash current sinks, the volt-
age observed on any single given output will be deter-
mined by the difference between V_OUT and the actual
forward voltage (V_F) of the flash LED being driven.
Any unused flash sink inputs must be connected to the
OUT pin; otherwise, the AAT2848 will operate continu-
ously in 2x charge pump mode regardless of the battery
voltage or V_F of the remaining diodes connected to the
current sinks. The S²Cwire serial interface at the FENS
input enables the charge pump and sets the flash cur-
rent sink levels.
The backlight and flash LED currents are controlled by a
combination of an external programming resistor from
BSET (for backlight) or FSET (for flash) to AGND and the
backlight or flash serial S²Cwire interface BENS or FENS.
The programming resistor sets the maximum LED cur-
rent for each channel, and the serial S²Cwire interface
controls the LED current relative to the maximum.
For backlight LEDs, the maximum channel current can
be set up to 30mA with a 10kΩ resistor connected at the
BSET pin of the AAT2848. Depending upon the applica-
tion and the white LEDs chosen, the preferred and most
accurate method for a backlight LED current control is to
choose R_BSET for the maximum backlight current required
by the application conditions and use the S²Cwire control
to set the backlight current to lower levels. The 32 levels
provided by the interface allows a smooth transition
between intermediate values. Table 1 and Figure 1 illus-
trate the current magnitude control from the S²Cwire
interface at the BENS pin, based on the maximum cur-
rent set by the R_BSET resistor.
For flash white LEDs, the maximum channel current can
be set up to 300mA with a 9.53kΩ resistor connected at
the FSET pin of the AAT2848. Depending upon the appli-
cation and the flash white LEDs chosen, the preferred
method for flash LED current control is to choose R_FSET for
the maximum flash current required by the application
conditions; use the S²Cwire control to set the backlight
current to lower levels. Table 2 and Figure 2 illustrate the
current magnitude control from the S²Cwire interface at
the FENS pin, based on the maximum current set by the
R_FSET resistor.
BENS Data
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
I_BLX (%)
100
97
93
90
87
83
80
77
73
70
67
63
60
57
54
51
47
44
41
38
35
32
28
25
22
19
16
13
10
7
3
1.5
R_BSET (Ω)
15k
(20mA Max)
Table 1: I_BLX (%) vs. BENS Data.
24
R_BSET = 15kΩ
20
16
12
8
4
0
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29 31
BENS Data (#)
Figure 1: BL1-BL4 Current Control Profile.
10
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2848.2008.05.1.0