AAT3151B
High Efficiency 1X/1.5X Charge Pump
For White LED Applications
drive can be changed successively to brighten or
dim LEDs in smooth transitions (e.g., to fade out) or
in abrupt steps, giving the user complete program-
mability and real-time control of LED brightness.
For each Max Current scale, there are 16 current
level settings separated from one another by
approximately 1dB. Code 1 is full-scale current and
Code 15 is full-scale current attenuated by roughly
14dB. Code 16 is reserved as a "no current" setting
(see Table 1).
The AAT3151B has an additional Low Current
mode with reduced quiescent current. This mode is
especially useful for low-current applications where
a continuous, low-current state is maintained. The
reduction in quiescent current significantly reduces
the impact due to maintaining a continuous back-
lighting state.
20mA Max
1
I
OUT
(mA)
20.0
17.8
15.9
14.3
12.7
11.1
10.2
8.9
7.9
7.0
6.3
5.7
5.1
4.4
4.1
0.0
AS
2
Cwire Serial Interface
The AS
2
Cwire single wire interface is used to set
the possible combinations of current levels and
LED channel states.
AS
2
Cwire relies on the number of rising edges of
the EN/SET pin to address and load the registers.
AS
2
Cwire latches data or address after the EN/SET
pin has been held high for time T
LAT
. Address or
data is differentiated by the number of EN/SET ris-
ing edges. Since the data registers are 4 bits each,
the differentiating number of pulses is 2
4
or 16, so
that Address 1 is signified by 17 rising edges,
Address 2 by 18 rising edges, and so forth. Data is
set to any number of rising edges between 1 and
including 16. A typical write protocol is a burst of
EN/SET rising edges, signifying a particular
address, followed by a pause with EN/SET held
high for the T
LAT
timeout period, a burst of rising
edges signifying data, and a T
LAT
timeout for the
data registers. Once an address is set, then multi-
ple writes to the corresponding data register are
allowed.
When EN/SET is held low for an amount of time
greater than T
OFF
, the AAT3151B enters shutdown
mode and draws less than 1µA from the supply.
Address 1 is the default address on the first rising
edge after the AAT3151B has been disabled.
Whenever shutdown mode is entered, all registers
are reset to 1.
Data
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
30mA Max 15mA Max
I
OUT
(mA)
I
OUT
(mA)
30.0
26.7
23.8
21.4
19.0
16.7
15.2
13.3
11.9
10.5
9.5
8.6
7.6
6.7
6.2
0.0
15.0
13.3
11.9
10.7
9.5
8.3
7.6
6.7
6.0
5.2
4.8
4.3
3.8
3.3
3.1
0.0
Table 1: Constant Current Programming
Levels (mA)
2
.
1. The device defaults to the 20mA Max scale. Use the Max Current Register to change the Max Scale.
2. There is an additional Low Current mode with currents down to 50µA. See the Low Current Register Settings section.
3151B.2007.09.1.0
9
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