AAT2846
High Current Charge Pump with Dual LDO
for Backlight and Flash Applications
interface. The backlight section has multiple current
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.
level scales and the maximum current level is fixed at
20mA or 30mA, depending on the scale chosen
through programming. The flash section maximum
current level is user programmable by an external set
resistor. The maximum flash current that can be sup-
ported by the device is 300mA/channel, or 600mA
total. This corresponds to a 280K set resistor value.
For maximum LED current lower than 300mA, use
a programming resistor greater than 280kΩ up to
1MΩ. Calculate the flash programming resistor
value using the equation:
When ENS is held low for a time greater than TOFF
(500µs), the AAT2846 enters shutdown mode and
draws less than 1µA of current from IN. At shut-
down, the data and address registers are reset to 0.
280k · 300mA
2
RFSET
=
Ω
AS Cwire Serial Interface Addressing
IFMAX
ENS
where IFMAX is the maximum flash LED current in mA.
Rising
Address Edges
Function
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.
0
1
17
18
Backlight Current BL1-BL6
Main Backlight Current
BL1-BL5
2
3
4
5
19
20
21
22
Sub Backlight Current BL6
Low Current Backlight
Flash Current FL1, FL2
Independent Flash On/Off
Control
Maximum Backlight Current
(Main and Sub)
Backlight Independent
Control
BL3-BL6 On/Off Control
BL1/BL2 On/Off Control
2
AS Cwire Serial Interface
12
15
29
32
The AAT2846 is dynamically programmable by the
2
2
AS Cwire single-wire interface. AS Cwire records
rising edges detected at the ENS pin to address
2
and load the data registers. AS Cwire latches data
Sub-2
Sub-3
19
20
or address after the ENS input has been held high
for time TLAT (500µs). Address or data is differenti-
ated by the number of ENS rising edges. Since the
data registers are 4 bits each, the differentiating
2
Table 1: AS Cwire Serial Interface Addressing.
4
number of pulses is 2 or 16, so that Address 0 is
Backlight Current Control (Address 0-3)
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 TLAT timeout
period, then a burst of rising edges signifying data,
and another TLAT timeout after the data has been
sent. Once an address is set, multiple writes to that
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
independently program subchannel BL6 only.
12
2846.2007.08.1.0
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
