AAT2856_08 Datasheet, PDF (10/18 Pages) Advanced Analogic Technologies – High Current Charge Pump with Dual LDO for Backlight Applications

PRODUCT DATASHEET
AAT2856
ChargePump^TM High Current Charge Pump with Dual LDO for Backlight Applications
The AAT2856 incorporates additional circuitry that opti-
mizes performance for exceptionally low backlight cur-
rent settings. A separate address is used to activate this
circuitry. To program the low current settings with
improved performance and efficiency, write to Address
3. Unlike Addresses 0-2, which have current level set-
tings according to Table 2 and Figure 2, Address 3 pos-
sesses a separate set of current levels described by the
Low Current Backlight settings found in Table 3.
Data
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
30mA Max (mA)
30.0
27.9
26.1
24.2
21.0
19.2
17.3
15.0
12.7
10.9
8.1
6.2
4.4
3.5
2.6
0
20mA Max (mA)
20.0
19.0
17.8
16.5
14.3
13.0
11.8
10.2
8.5
7.3
5.4
4.1
2.9
2.2
1.6
0
Table 2: Data for the Backlight Current Level,
Addresses 0-3.
Data
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
Main Current
On
No
No
No
No
No
No
No
No
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Sub Current
On
No
No
No
No
Yes
Yes
Yes
Yes
No
No
No
No
Yes
Yes
Yes
Yes
Current
(μA)
0
0
0
0
95
500
950
1900
95
500
950
1900
95
500
950
1900
Table 3: Low-Level Backlight Current,
Address 3, FS = 20mA Range.
35
30
30mA FS
25
20
15
20mA FS
10
5
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Data Code
Figure 2: Data Code for Address 0-3 vs.
Backlight Current Level.
Maximum Backlight Current
(Address 12)
There are two separate current level scales that apply to
Addresses 0-2: 20mA and 30mA. According to the
Maximum Backlight Current setting at Address 12, only
one of the two scales can be active at any given time
and never both. By default, the 20mA scale is active on
startup. To change to the 30mA scale, or go back to the
20mA scale, write to Address 12.
Since only one of the scales can be active at any given
time, the 20mA and 30mA scales cannot be mixed
between main and sub. When setting Address 12 to the
30mA scale, only current levels from that scale can be
mixed between main and sub. When changing maximum
current scales, the data remains constant regardless of
scale. When the maximum current scale is changed, the
previously stored data value will remain constant but the
current value will change due to the different current
values on the separate maximum current scales.
Data
1
2
Maximum Current Scale
20mA
30mA
Table 4: Address 12 Maximum Current Scale.
Backlight Independent Channel Control
(Address 15)
The AAT2856 has a unique independent channel control
mode whereby individual backlight LED channels can be
enabled and disabled to form a custom arrangement of
active channels.
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2856.2008.02.1.3