PRODUCT DATASHEET
AAT3103
ChargePumpTM
3-Channel Charge-Pump LED Driver
Applications Information
35
RSET = 9.53k
30
LED Selection
25
RSET = 14.3k
The AAT3103 is specifically intended for driving WLEDs.
However, the device design will allow the AAT3103 to
drive most types of LEDs with forward voltage specifica-
tions ranging from 2.2V to 4.7V. LED applications may
include mixed arrangements for display backlighting,
keypad display, and any other application needing a con-
stant current sink generated from a varying input volt-
age. Since the D1 to D3 constant current sources are
matched with negligible supply voltage dependence, the
constant current channels will be matched regardless of
the specific LED forward voltage (VF) levels.
20
RSET = 19.1k
15
RSET = 28.7k
10
5
0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16
S2C Wire Interface Data Code
Figure 5: AAT3103-1 LED Current Control Profile
at Different RSET Values.
The internal charge pump and low dropout current
sources in the AAT3103 maximize performance and
make it capable of driving LEDs with high forward volt-
ages. Multiple channels can be combined to obtain a
higher LED drive current without complication.
Use the following formula to calculate the AAT3103-3 full
scale LED current:
1.2
ILED_FS
=
· 4 · 48
RSET
Constant Current Setting
For example, an 11.5kΩ 1% resistor is used to achieve
The LED full scale current is controlled by the RSET resis-
tor. The following formula can be used to calculate the
AAT3103-1/2/4 full scale LED current:
20mA full scale LED current operation.
Device Switching Noise Performance
The AAT3103 operates at a fixed frequency of approxi-
mately 0.9MHz to control noise and limit harmonics that
can interfere with the RF operation of mobile communi-
cation devices. Back-injected noise appearing on the
input pin of the charge pump is 20mV peak-to-peak,
typically ten times less than inductor-based DC/DC boost
converter WLED backlight solutions. The AAT3103's soft-
start feature prevents noise transient effects associated
with inrush currents during start-up of the charge pump
circuit.
1.2
RSET
ILED_FS
=
· 4 · 60
Table4showstheRSET resistorvaluefortheAAT3103-1/2/4
for various LED full-scale current levels. For maximum
accuracy, a 1% tolerance resistor is recommended.
ILED_FS (mA)
RSET (kΩ)
30.2
20.1
15.1
10.0
9.53
14.3
19.1
28.7
Shutdown
To activate the shutdown operation, the EN/SET input for
the AAT3103-1/-2 should be pulsed low for longer than
tOFF (500μs). For the 3103-4 PWM options, shutdown
operation is enabled when the EN/PWM input is pulsed
low longer than 500μs. In this state, the AAT3103 typi-
cally draws less than 1μA from the input. Registers are
reset to 0 in shutdown.
Table 4: Maximum LED Current and RSET Resistor
Values (1% Resistor Tolerance) for the AAT3103.
The S2C interface rising edges control the LED current
from full scale to the LSB. For the AAT3103-1, 16 steps
are employed. Figure 5 shows the LED current of the
AAT3103-1 at different RSET values.
w w w . a n a l o g i c t e c h . c o m
3103.2008.03.1.0
11
AAT [ ADVANCED ANALOG TECHNOLOGY, INC. ]
