AAT2847
Four-Channel Backlight Driver with Dual LDOs
identify/target a particular address followed by
EN/SET being held logic high for the TLAT timeout
period to latch the address value in the address
register, then another burst of rising edges that sig-
nify data with the accompanying TLAT timeout peri-
od to latch the data value in the data register. Once
an address is set, then multiple writes to the corre-
30.0
25.0
20.0
15.0
10.0
5.0
Address 0
Address 4
sponding 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
0.0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16
1
2
3
4
than TOFF (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.
Code
Figure 1: LED Current Control Profile.
2
AS Cwire Serial Interface
2
AS Cwire Serial Interface Addressing
Each white LED channel input on the AAT2847
2
(D1-D4) is controlled by AnalogicTech's AS Cwire
EN/SET
2
serial digital interface. The AS Cwire interface uses
Address Edges
Addressed Register
D1-D4 Current Control
Current Scale
Low Current Control
Independent LED Control
the number of rising edges on the EN/SET pin to
address and load the LED configuration registers.
0
3
4
5
17
20
21
22
2
AS Cwire latches data or addresses after the
EN/SET pin has been held logic high for longer
than TLAT (500µs). Addresses and data are differ-
entiated by the number of EN/SET rising edges.
Since the data registers are 4 bits each, the differ-
2
Table 1: AS Cwire Serial Interface Addressing.
4
entiating number of pulses is 2 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.
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 cur-
rent level by writing to Address 0 followed by any
Data between, and including, 1 to 16.
A typical write protocol consist of the following:
First a burst of EN/SET rising edges that
Address
THI
Data
TLAT
TLO
TLAT
EN/SET
1
2
19
0
20
1
2 . . .
n ≤ 16
Address
DATA3
DATA0
3
1
1
n
2
Figure 2: AS Cwire Serial Interface Timing.
12
2847.2007.09.1.0
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
