AAT2846_08 Datasheet, PDF (10/22 Pages) Advanced Analogic Technologies – High Current Charge Pump with Dual LDO for Backlight and Flash Applications

PRODUCT DATASHEET
AAT2846
ChargePump^TM High Current Charge Pump with Dual LDO for Backlight and Flash Applications
The backlight and flash LED current levels are dynami-
cally controllable by the AS²Cwire single-wire 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 program-
ming. The flash section maximum current level is user
programmable by an external set resistor. The maximum
flash current that can be supported 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 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.
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 differentiated 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 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 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 pro-
grammed and backlight channels 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 shutdown, the data
and address registers are reset to 0.
EN/SET
Address
Address
T _HI
T _LO
T_LAT
1
2
17
18
0
Data
T_LAT
1
2 . . . n ≤ 16
1
Data Reg 1
0
n
Data Reg 2
0
Figure 1: AS²Cwire Serial Interface Timing.
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2846.2008.03.1.1