AAT2846 Datasheet, PDF (12/25 Pages) Advanced Analogic Technologies – High Current Charge Pump with Dual LDO for Backlight and Flash Applications

AAT2846
High Current Charge Pump with Dual LDO
for Backlight and Flash Applications
interface. The backlight section has multiple current
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:
R_FSET =
280k · 300mA
I_FMAX
Ω
where I_FMAX is the maximum flash LED current in mA.
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.
AS²Cwire Serial Interface
The AAT2846 is dynamically programmable by the
AS²Cwire single-wire interface. AS²Cwire records
rising edges detected at the ENS pin to address
and load the data registers. AS²Cwire latches data
or address after the ENS input has been held high
for time T_LAT (500µs). Address or data is differenti-
ated by the number of ENS rising edges. Since the
data registers are 4 bits each, the differentiating
number of pulses is 2⁴ or 16, so that Address 0 is
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_LAT timeout
period, then a burst of rising edges signifying data,
and another T_LAT timeout after the data has been
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 greater than T_OFF
(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.
AS²Cwire Serial Interface Addressing
Address
0
1
2
3
4
5
12
15
Sub-2
Sub-3
ENS
Rising
Edges
17
18
19
20
21
22
29
32
19
20
Function
Backlight Current BL1-BL6
Main Backlight Current
BL1-BL5
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
Table 1: AS²Cwire Serial Interface Addressing.
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
independently program subchannel BL6 only.
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2846.2007.08.1.0