AAT2856_08 Datasheet, PDF (11/18 Pages) Advanced Analogic Technologies – High Current Charge Pump with Dual LDO for Backlight Applications

PRODUCT DATASHEET
AAT2856
ChargePump^TM High Current Charge Pump with Dual LDO for Backlight Applications
To enable independent channel control mode, write Data
8 to Address 15. To exit individual mode control, the
AAT2856 state machine can be reset by strobing ENS
low and holding ENS low longer than the AS²Cwire’s t_OFF
latch time.
Data
8
Individual Backlight Control
On
Table 5: Address 15, Independent
Backlight Control.
With independent channel control enabled, the functional-
ity of Addresses 2 and 3 will conform to what is described
in Tables 8 and 9. Also Address 0 is no longer applicable
after independent channel control has been enabled. As
indicated by the possible settings listed in the tables, any
combination of backlight channels can be enabled and
disabled. The original functionality (Sub Backlight Current
BL6 and Low Current Backlight) of Addresses 2 and 3 are
no longer available unless the internal state machine has
been reset to default mode operation (when ENS is logic
low for >500μs). The functionality of the maximum back-
light current scale (Address 12) is unmodified by the
enabling of independent channel control.
The LDO enables are always independent of AS²Cwire
programming.
Data
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
BL6
Off
Off
Off
Off
Off
Off
Off
Off
On
On
On
On
On
On
On
On
BL5
Off
Off
Off
Off
On
On
On
On
Off
Off
Off
Off
On
On
On
On
BL4
Off
Off
On
On
Off
Off
On
On
Off
Off
On
On
Off
Off
On
On
BL3
Off
On
Off
On
Off
On
Off
On
Off
On
Off
On
Off
On
Off
On
Table 6: Address 2 with Independent Channel
Control Enabled: BL3-BL6 On/Off Control.
Data
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
BL2
Off
Off
Off
Off
Off
Off
Off
Off
On
On
On
On
On
On
On
On
BL1
Off
Off
Off
Off
On
On
On
On
Off
Off
Off
Off
On
On
On
On
Table 7: Address 3 with Independent Channel
Control Enabled: BL1 and BL2 On/Off Control.
Low Dropout Regulators
The AAT2856 includes two independent LDO linear regu-
lators. The regulators operate from a 2.7V to 5.5V input
voltage at IN. The AAT2856 supplies separate LDO
enable inputs (ENA and ENB) to control individually the
operation of the LDOs. The LDO output voltages are set
through resistive voltage dividers from the output (OUTA
or OUTB) to the feedback input (FBA or FBB). The regu-
lator controls the output voltage such that the voltage
divider output is at the 1.2V feedback threshold. The low
200mV dropout voltage at 200mA load current allows
the regulator to maintain output voltage regulation.
Each LDO regulator can supply up to 200mA continuous
current to the load. They include current limiting and
thermal overload protection to prevent damage to the
load or to the LDOs.
2856.2008.02.1.3
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