AAT3151
High Efficiency 1X/1.5X/2X Charge Pump
For White LED Applications
AS2Cwire Serial Interface Timing
Address
Data
THI
TLAT
TLO
TLAT
EN/SET
Address
1
2
17
18
1
2 . . .
n <= 16
2
1
1
1
n
Data Reg 1
Data Reg 2
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-channel, giving 16 settings for each.
The main and sub-channel are programmed to the
same constant current level by using Address 1. Use
Addresses 2 and 3 to program the main and sub-
channel independently. Use Address 4 to program
the Max Current register, which sets the Max
Current scale. Address 5 programs the Low Current
register. The Low Current register controls the effi-
cient Low Current mode.
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 AAT3151 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 col-
umn. Next, to change to a different setting on the
30mA Max scale, address the D1-D4 register with 17
rising edges. Program the new constant 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 1,
2, or 3, changing the data for Addresses 1-3 will
result in the corresponding values found in 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 Table 2 for the current level set-
tings and main/sub-configurations that result.
The AAT3151 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 particularly use-
ful for applications requiring an "always on" condi-
tion, such as transmissive displays. As an exam-
ple, 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-D4
Current
2
3
4
5
18
19
20
21
1: D1-D3 Current
2: D4 Current
3: Max Current
4: Low Current
Table 2: Low Current Register Settings.
10
3151.2005.12.1.7
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