PRODUCT DATASHEET
AAT2846
ChargePumpTM High Current Charge Pump with Dual LDO for Backlight and Flash Applications
AS2Cwire Serial Interface
The backlight and flash LED current levels are dynami-
cally controllable by the AS2Cwire single-wire interface.
The AAT2846 is dynamically programmable by the
The backlight section has multiple current level scales
AS2Cwire single-wire interface. AS2Cwire records rising
and the maximum current level is fixed at 20mA or
edges detected at the ENS pin to address and load the
30mA, depending on the scale chosen through program-
data registers. AS2Cwire latches data or address after the
ming. The flash section maximum current level is user
ENS input has been held high for time TLAT (500µs).
programmable by an external set resistor. The maximum
Address or data is differentiated by the number of ENS
flash current that can be supported by the device is
rising edges. Since the data registers are 4 bits each, the
300mA/channel, or 600mA total. This corresponds to a
differentiating number of pulses is 24 or 16, so that
280K set resistor value.
Address 0 is identified by 17 rising edges, Address 1 by
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:
18 rising 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 iden-
tifying 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 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 pro-
grammed and backlight channels BL1-BL6 will turn-on
according to the number of data edges applied.
280k · 300mA
RFSET
=
Ω
IFMAX
where IFMAX 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 con-
troller monitors the sink voltage and, if it is connected to
OUT, then the controller determines that the current sink
is not used or that the LED is shorted. In either case, the
controller turns off the affected current sink.
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 shutdown, the data
and address registers are reset to 0.
Address
Data
THI
TLAT
TLO
TLAT
EN/SET
1
2
17
0
18
1
2 . . .
n ≤ 16
Address
Data Reg 1
Data Reg 2
1
0
0
n
Figure 1: AS2Cwire Serial Interface Timing.
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2846.2008.03.1.1
ANALOGICTECH [ ADVANCED ANALOGIC TECHNOLOGIES ]
