AAT2848 Analogic Corporation, AAT2848 Datasheet - Page 10

• Manufacturer Part Number: AAT2848
• Manufacturer: Analogic Corporation

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
forward voltage (V
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
current sinks. The S
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 S
The programming resistor sets the maximum LED cur-
rent for each channel, and the serial S
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
by the application conditions and use the S
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 S
interface at the BENS pin, based on the maximum cur-
rent set by the R
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
the maximum flash current required by the application
conditions; use the S
current to lower levels. Table 2 and Figure 2 illustrate the
current magnitude control from the S
the FENS pin, based on the maximum current set by the
R
10
ChargePump
FSET
resistor.
BSET
F
for the maximum backlight current required
of the remaining diodes connected to the
BSET
TM
F
) of the flash LED being driven.
2
resistor.
Cwire serial interface at the FENS
2
Cwire control to set the backlight
2
High-Current Charge Pump For Backlight Display and Flash Applications
Cwire interface BENS or FENS.
OUT
2
Cwire interface at
2
and the actual
Cwire interface
2
Cwire control
w w w . a n a l o g i c t e c h . c o m
2
FSET
Cwire
for
BENS Data
Figure 1: BL1-BL4 Current Control Profile.
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
1
2
3
4
5
6
7
8
9
24
20
16
12
8
4
0
Table 1: I
1
3
5
7
9
BLX
PRODUCT DATASHEET
11 13 15 17 19 21 23 25 27 29 31
(%) vs. BENS Data.
I
BENS Data (#)
BLX
100
1.5
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
(%)
AAT2848
R
2848.2008.05.1.0
BSET
= 15k
(20mA Max)
R
BSET
15k
(Ω)