AAT2801 Datasheet, PDF (15/20 Pages) Advanced Analogic Technologies – Multi-Mode Charge Pump for White LED Backlight and Flash Applications

AAT2801
Multi-Mode Charge Pump for
White LED Backlight and Flash Applications
Constant Current Source Output
Nominal Programming Levels (mA)
Code
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
I_OU(mT (Aty)p)
0.0
0.1
0.2
0.4
0.5
0.7
1.1
1.8
2.0
2.2
2.5
2.8
3.2
3.5
4.0
4.5
Code
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
I_OU(mT (Aty)p)
5.1
5.6
6.4
7.2
8.1
9.2
10.2
11.5
13.1
14.7
16.6
18.6
20.9
23.6
26.6
30.0
S²Cwire Serial Interface
The current source output magnitude is controlled
by the EN/SET pin, using AnalogicTech's S²Cwire
interface. The interface records rising edges of
the EN/SET pin and decodes them into 32 indi-
vidual current level settings each 1dB apart with
Code 1 reserved for no current. Once EN/SET
has been held in the logic high state for time T_LAT,
the programmed current is seen at the current
source outputs, and the internal data register is
reset to 0. For subsequent current level pro-
gramming, the number of rising edges correspon-
ding to the desired code must be entered on the
EN/SET pin.
When EN/SET is held low for an amount of time
greater than T_OFF, the AAT2801 enters into shut-
down mode and draws less than 1µA from V_IN.
The internal data register is reset to 0 during shut-
down.
S²Cwire Serial Interface Timing Diagram
EN/SET
Data Reg
THI
TLO
TLAT
1
2
n-1 n <= 32
0
TOFF
n
0
Termination of Unused Current Source
Outputs
If any outputs (D1 to D4) are not used, they should
be terminated by connecting the respective unused
output directly to ground. This is required to assure
correct charge pump mode operation. If a given
unused output is not terminated to ground, it will
appear to the respective output’s feedback control
as an infinite impedance load and the unused con-
stant current source will be set to maximum volt-
age. Although no current flows from the unused
current source, the voltage sensed at that node
could force the charge pump control to activate the
2801.2006.04.1.3
charge pump when it is not necessary. To prevent
this effect, simply connect unused constant current
source outputs to ground.
LED Selection
The AAT2801 is specifically intended for driving
white LEDs. However, the device design will allow
the AAT2801 to drive most types of LEDs with for-
ward voltage specifications ranging from 2.0V to
4.3V. Since the D1 to D4 output current sources
are matched with negligible voltage dependence,
the LED brightness will be matched regardless of
the specific LED forward voltage (V_F) levels.
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