AAT2848 Analogic Corporation, AAT2848 Datasheet - Page 11

• Manufacturer Part Number: AAT2848
• Manufacturer: Analogic Corporation

S
The S
AAT2848 exhibits flexible timing in that data can be
clocked-in at speeds ranging from 15kHz to higher than
1MHz.
The S
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
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.
ChargePump
2848.2008.05.1.0
2
FENS
Data
Cwire Serial Interface
1
2
3
4
5
6
7
8
Figure 2: FL1-FL2 Current Control Profile.
2
2
Cwire serial interface recognizes rising edges at
Cwire single-wire serial interface used in the
240
200
160
120
80
40
Table 2: I
0
1
(%)
I
100
94
87
81
73
67
60
53
FLX
3
TM
(206mA
FLX
R
14.3k
Max)
5
(Ω)
FSET
(%) vs. FENS Data.
High-Current Charge Pump For Backlight Display and Flash Applications
FENS Data (#)
7
FENS
Data
9
10
11
12
13
14
15
16
9
LAT
11
R
(500μs), the pro-
FSET
(%)
I
13
46
40
34
27
20
13
FLX
6
3
= 14.3k
15
w w w . a n a l o g i c t e c h . c o m
(206mA
14.3k
R
Max)
(Ω)
FSET
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.
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:
where Flash Timeout is in seconds and C
example, for a 0.33μF capacitor:
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
enters shutdown mode and draws less than 1μA from
V
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
following equation:
R
I
BLED
IN
BSET
. Both internal backlight and flash data registers are
= Backlight LED Current
= Backlight LED Current Programming Resistor
Flash Timeout = 3.9 s/μF · 0.33μF = 1.3s
Flash Timeout = 3.9 s/μF · C
PRODUCT DATASHEET
R
BSET
=
AAT2848
I
300
OFF
BLED
(500μs), the AAT2848
BSET
FLTMR
resistor with the
FLTMR
is in μF. For
Flash
11