AAT2847_08 Datasheet, PDF (12/20 Pages) Advanced Analogic Technologies – Four-Channel Backlight Driver with Dual LDOs

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PRODUCT DATASHEET
AAT2847
Four-Channel Backlight Driver with Dual LDOs
30.0
25.0
20.0
15.0
10.0 Address 0
5.0
Address 4
0.0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 1 2 3 4
Code
Figure 1: LED Current Control Profile.
AS²Cwire Serial Interface
Each white LED channel input on the AAT2847 (D1-D4) is
controlled by AnalogicTech’s AS²Cwire serial digital inter-
face. The AS²Cwire interface uses the number of rising
edges on the EN/SET pin to address and load the LED
configuration registers. AS²Cwire latches data or address-
es after the EN/SET pin has been held logic high for lon-
ger than T_LAT (500µs). Addresses and data are differenti-
ated by the number of EN/SET rising edges. Since the
data registers are 4 bits each, the differentiating number
of pulses is 24 or 16, so that Address 0 is signified by 17
rising edges, Address 1 by 18 rising edges, Address 2 by
19 rising edges, and so on. Data is set to any number of
rising edges between, and including, 1 to 16.
A typical write protocol consist of the following: First a
burst of EN/SET rising edges that identify/target a par-
ticular address followed by EN/SET being held logic high
for the T_LAT timeout period to latch the address value in
the address register, then another burst of rising edges
that signify data with the accompanying T_LAT timeout
period to latch the data value in the data register. Once
an address is set, then multiple writes to the correspond-
ing data register are allowed without having to write to
the address for every value change in the data register.
When EN/SET is held low longer than T_OFF (500µs), the
AAT2847 enters shutdown mode operation and draws less
than 1µA from the input supply voltage. Data and address
registers are cleared (0 for the address register and 1 for
the data registers) in shutdown mode operation.
AS²Cwire Serial Interface Addressing
Address
0
3
4
5
EN/SET Edges
17
20
21
22
Addressed Register
D1-D4 Current Control
Current Scale
Low Current Control
Independent LED Control
Table 1: AS²Cwire Serial Interface Addressing.
Current Operation (Address 0)
Use Address 0 to program all four LED channels with the
current values in Table 2. All four white LED channels are
programmed to the same current level by writing to
Address 0 followed by any Data between, and including,
1 to 16.
Current Scale (Address 3)
The AAT2847 has three selectable current scales for the
four white LED channels: 30mA, 20mA, and 15mA. Only
one of the three current scales can be active at any given
time. By default, the 20mA current scale is active upon
start-up. To change to the 30mA or 15mA current scale,
or go back to the 20mA scale, write to Address 3 with
the appropriate Data between, and including, 1 to 3. To
enable low current mode, write Data 4 to Address 3. Low
current mode results in the four white LED channels
reverting to the current set by the low current settings
in Address 4.
Data
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
30mA
Scale
30.0
28.5
26.6
25.2
23.3
21.8
19.8
18.5
16.5
15.0
13.1
11.6
9.8
8.3
6.3
4.8
20mA
Scale
20.0
19.0
17.7
16.8
15.5
14.5
13.2
12.3
11.0
10.0
8.7
7.7
6.5
5.5
4.2
3.2
15mA
Scale
15.0
14.3
13.3
12.6
11.6
10.9
9.9
9.2
8.3
7.5
6.5
5.8
4.9
4.1
3.2
2.4
Table 2: Current Settings—Address 0.
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2847.2008.05.1.2