PRODUCT DATASHEET
AAT2848
TM
ChargePump
High-Current Charge Pump For Backlight Display and Flash Applications
The AAT2848 features separate control interfaces for
FENS
Data
IFLX
(%)
RFSET
(Ω)
FENS
Data
IFLX
(%)
RFSET
(Ω)
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.
1
2
3
4
5
6
7
8
100
94
87
81
73
67
60
53
9
46
40
34
27
20
13
6
10
11
12
13
14
15
16
The flash has 16 current level settings; again, each step
as a percentage of the maximum flash current set by the
FSET resistor.
14.3k
(206mA
Max)
14.3k
(206mA
Max)
Flash Timeout Functionality
3
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
Table 2: IFLX (%) vs. FENS Data.
240
RFSET = 14.3kΩ
200
160
120
80
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:
40
0
1
3
5
7
9
11
13
15
Flash Timeout = 3.9 s/μF · CFLTMR
FENS Data (#)
where Flash Timeout is in seconds and CFLTMR is in μF. For
example, for a 0.33μF capacitor:
Figure 2: FL1-FL2 Current Control Profile.
Flash Timeout = 3.9 s/μF · 0.33μF = 1.3s
S2Cwire Serial Interface
To disable the flash timer, connect the FLTMR pin to
AGND.
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.
When both the BENS and the FENS inputs are strobed
and held low for longer than tOFF (500μs), the AAT2848
enters shutdown mode and draws less than 1μA from
VIN. Both internal backlight and flash data registers are
cleared to zero when in shutdown.
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.
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 RBSET resistor with the
following equation:
Once the data at BENS or FENS has been held in the
logic high state for longer than tLAT (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.
300
IBLED
RBSET
=
RBSET = Backlight LED Current Programming Resistor
IBLED = Backlight LED Current
w w w . a n a l o g i c t e c h . c o m
2848.2008.05.1.0
11
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