AAT2856 AAT, AAT2856 Datasheet - Page 11

• Manufacturer Part Number: AAT2856
• Description: High Current Charge Pump
• Manufacturer: AAT

scales and the maximum current level is fixed at
20mA or 30mA, depending on the scale chosen
through programming.
If any one of the backlight or flash current sinks is
not used, connect that current sink to OUT. The
current controller monitors the sink voltage and, if it
is connected to OUT, then the controller deter-
mines that the current sink is not used or that the
LED is shorted. In either case, the controller turns
off the affected current sink.
AS
The AAT2856 is dynamically programmable by the
AS
rising edges detected at the ENS pin to address
and load the data registers. AS
or address after the ENS input has been held high
for time t
ated by the number of ENS rising edges. Since the
data registers are 4 bits each, the differentiating
number of pulses is 2
identified by 17 rising edges, Address 1 by 18 ris-
ing edges, Address 2 by 19 rising edges, etc. Data
is set to any number of rising edges between 1 and
16. A typical write protocol is a burst of ENS rising
edges identifying a particular address, followed by
a pause with ENS held high for the t
period, then a burst of rising edges signifying data,
and another t
sent. Once an address is set, multiple writes to that
address are allowed since the address is not reset
after each write. Address edges are needed when
changing the address, or writing to an address
other than the default after shutdown. Address 0 is
the default address after shutdown. If the part is
enabled with only data edges and no address, then
Address 0 will be programmed and backlight chan-
nels BL1-BL6 will turn-on according to the number
of data edges applied.
When ENS is held low for a time longer than t
(500µs), the AAT2856 enters shutdown mode and
draws less than 1µA of current from IN. At shut-
down, the data and address registers are reset to 0.
2856.2007.06.1.0
2
Cwire single-wire interface. AS
2
Cwire Serial Interface
LAT
(500µs). Address or data is differenti-
LAT
timeout after the data has been
4
or 16, so that Address 0 is
2
Cwire latches data
2
Cwire records
LAT
timeout
OFF
Dual LDO for BacklightApplications
AS
Backlight Current Control (Address 0-3)
Use Addresses 0-3 to program all six backlight LED
channels. All six backlight channels are pro-
grammed to the same current level by writing
Address 0 followed by any Data between 1 and 16.
To program only the main channels BL1 through
BL5, use Address 1. Similarly, use Address 2 to
program only the sub channel BL6 independently.
Table 1: AS
Table 2: Data for the Backlight Current Level
Address
High Current Charge Pump with
Data
Sub-2
Sub-3
2
10
12
13
14
15
16
11
1
2
3
4
5
6
7
8
9
Cwire Serial Interface Addressing
12
15
0
1
2
3
30mA Max (mA)
2
Cwire Serial Interface Addressing.
Rising
Edges
ENS
17
18
19
20
29
32
19
20
30.0
27.9
26.1
24.2
21.0
19.2
17.3
15.0
12.7
10.9
(Address 0-3).
8.1
6.2
4.4
3.5
2.6
0
Maximum Backlight Current
Backlight Current BL1-BL6
Sub Backlight Current BL6
BL3-BL6 On/Off Control
BL1/BL2 On/Off Control
Main Backlight Current
Backlight Independent
Low Current Backlight
(Main and Sub)
20mA Max (mA)
Function
BL1-BL5
Control
AAT2856
20.0
19.0
17.8
16.5
14.3
13.0
10.2
11.8
8.5
7.3
5.4
4.1
2.9
2.2
1.6
0
11