AAT2803
Six-Channel White LED Backlight
Charge Pump with Flash
AS2Cwire Serial Interface Timing
Address
THI
Data
TLAT
TLO
TLAT
EN/SET
1
2
17
1
18
1
2 . . .
n <= 16
2
Address
Data Reg 1
Data Reg 2
1
1
n
AS2Cwire Addressing
Max Current and Low Current Registers
Five addresses are available to enable all of the
part's functionality. Two 4-bit registers control the
main and sub-channels, giving 16 settings for each.
The main and sub-channels are programmed to the
same constant current level by using Address 1.
Use Addresses 2 and 3 to program the main and
sub-channels independently. Use Address 4 to pro-
gram the Max Current register, which sets the Max
Current scale. Lastly, Address 5 programs the Low
Current register. The Low Current register controls
the efficient Low Current mode. When the Max
Current register is programmed to 1, 2, or 3, chang-
ing the data for Addresses 1-3 will result in the cor-
responding values found in the Constant Current
Programming Levels table.
Use the Max Current and Low Current registers to
program constant current settings outside of the
20mA Max scale. By default (without changing the
Max Current register), the backlight charge pump
operates in the 20mA Max scale (see Constant
Current Programming Levels). For example, to
change to the 30mA Max scale, address the Max
Current register with 20 rising edges and pause for
TLAT. Program the Max Current register with 2 rising
edges and pause for TLAT. The part will next operate
in the same Data row, but for the setting found in the
30mA Max column. Next, to change to a different
setting on the 30mA Max scale, address the D1-D6
register with 17 rising edges. Program the new con-
stant current level with 1-16 rising edges. The part
will update to the new Data setting according to the
Constant Current Programming Levels table.
When the Max Current register is programmed to 4,
the part is programmed to operate in Low Current
mode and the Data for Addresses 1-3 is irrelevant.
In Low Current mode, the Low Current register
takes precedence. See the Low Current Register
Settings table below for the current level settings
and main/sub-configurations that result.
The backlight charge pump has a distinct Low
Current mode with ultra-low quiescent current. For
drive currents of 2mA or less, the part operates with
significantly reduced quiescent current. This is par-
ticularly useful for applications requiring an "always
on" condition such as transmissive displays. As an
example, to change to Low Current mode, address
the Max Current register with 20 rising edges and
pause for TLAT. Program the Max Current register
with 4 rising edges and pause for TLAT. Address the
Low Current register with 21 rising edges and
pause for TLAT. Program the Low Current register
with 1-16 rising edges. The part will update to the
new Low Current mode setting and operate with
significantly reduced quiescent current.
EN/SET
Edges
Addressed
Register
Address
1
17
1&2: D1-D6
Current
2
3
4
5
18
19
20
21
1: D1-D4 Current
2: D5-D6 Current
3: Max Current
4: Low Current
2803.2006.12.1.6
13
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
