PRODUCT DATASHEET
AAT2848
TM
ChargePump
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 VOUT and the actual
forward voltage (VF) of the flash LED being driven.
BENS Data
IBLX (%)
RBSET (Ω)
1
2
3
4
5
6
7
8
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
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 VF 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.
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
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.
15k
(20mA Max)
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 RBSET 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 RBSET resistor.
3
1.5
Table 1: IBLX (%) vs. BENS Data.
24
RBSET = 15kΩ
20
16
12
8
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 RFSET 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
RFSET resistor.
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.
w w w . a n a l o g i c t e c h . c o m
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2848.2008.05.1.0
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
