AAT2848 Datasheet, PDF (11/19 Pages) Advanced Analogic Technologies – High-Current Charge Pump For Backlight Display and Flash Applications

ChargePump^TM
PRODUCT DATASHEET
AAT2848
High-Current Charge Pump For Backlight Display and Flash Applications
FENS
Data
1
2
3
4
5
6
7
8
I_FLX
(%)
100
94
87
81
73
67
60
53
R_FSET
(Ω)
14.3k
(206mA
Max)
FENS
Data
9
10
11
12
13
14
15
16
I_FLX
(%)
46
40
34
27
20
13
6
3
R_FSET
(Ω)
14.3k
(206mA
Max)
Table 2: I_FLX (%) vs. FENS Data.
240
200
160
120
80
40
0
1
3
R_FSET = 14.3kΩ
5
7
9
11
13
15
FENS Data (#)
Figure 2: FL1-FL2 Current Control Profile.
S²Cwire Serial Interface
The S²Cwire single-wire serial interface used in the
AAT2848 exhibits flexible timing in that data can be
clocked-in at speeds ranging from 15kHz to higher than
1MHz.
The S²Cwire serial interface recognizes rising edges at
both the BENS pin and at the FENS pin. For setting the
backlight current level, data applied at the AAT2848’s
BENS input is decoded into 32 different levels. For set-
ting the flash current level, data applied at the AAT2848’s
FENS input is decoded into 16 different levels. After data
is supplied, the BENS and the FENS inputs pins are held
high to latch the data.
Once the data at BENS or FENS has been held in the
logic high state for longer than t_LAT (500μs), the pro-
grammed backlight or flash current becomes active and
the internal backlight and flash data registers are
latched. To adjust the backlight and/or flash current lev-
els once programmed, the requisite number of rising
edges corresponding to the desired code must be applied
at the BENS or the FENS pin.
The AAT2848 features separate control interfaces for
backlight and flash current control. The backlight current
features 32 current steps, each step as a percentage of
the maximum backlight current set by the BSET resistor.
The flash has 16 current level settings; again, each step
as a percentage of the maximum flash current set by the
FSET resistor.
Flash Timeout Functionality
The AAT2848 contains an internal flash mode operation
timeout safety circuit. The purpose of this timeout circuit
is to prevent any thermal damage to the flash white LED
when flash mode operation is unable to be disabled by
the embedded microprocessor/microcontroller. Flash
mode operation is initiated by strobing the FENS pin low-
to-high, this also initiates the flash timer circuit which
can be programmed via an external capacitor at the
FLTMR pin. The flash timeout period can be calculated
using the following equation:
Flash Timeout = 3.9 s/μF · C_FLTMR
where Flash Timeout is in seconds and C_FLTMR is in μF. For
example, for a 0.33μF capacitor:
Flash Timeout = 3.9 s/μF · 0.33μF = 1.3s
To disable the flash timer, connect the FLTMR pin to
AGND.
When both the BENS and the FENS inputs are strobed
and held low for longer than t_OFF (500μs), the AAT2848
enters shutdown mode and draws less than 1μA from
V_IN. Both internal backlight and flash data registers are
cleared to zero when in shutdown.
Backlight/Flash LED Current Setting
The maximum backlight and flash LED currents are set,
or programmed, with external resistors. The backlight
LED current is programmed by the R_BSET resistor with the
following equation:
300
R_BSET = _IBLED
R_BSET = Backlight LED Current Programming Resistor
I_BLED = Backlight LED Current
2848.2008.05.1.0
www.analogictech.com
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