AAT3103 Datasheet, PDF (11/17 Pages) Advanced Analog Technology, Inc. – 3-Channel Charge-Pump LED Driver

ChargePump^TM
Applications Information
LED Selection
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 (V_F) levels.
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.
Constant Current Setting
The LED full scale current is controlled by the R_SET resis-
tor. The following formula can be used to calculate the
AAT3103-1/2/4 full scale LED current:
I_{LED_FS}
=
1.2
R_SET
·
4
·
60
Table 4 shows the R_SET resistor value for the AAT3103-1/2/4
for various LED full-scale current levels. For maximum
accuracy, a 1% tolerance resistor is recommended.
I_{LED_FS} (mA)
30.2
20.1
15.1
10.0
R_SET (kΩ)
9.53
14.3
19.1
28.7
Table 4: Maximum LED Current and R_SET 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 R_SET values.
PRODUCT DATASHEET
AAT3103
3-Channel Charge-Pump LED Driver
35
30
R_SET = 9.53k
25
R_SET = 14.3k
20
R_SET = 19.1k
15
10
R_SET = 28.7k
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 R_SET Values.
Use the following formula to calculate the AAT3103-3 full
scale LED current:
I_{LED_FS}
=
1.2
R_SET
·
4
·
48
For example, an 11.5kΩ 1% resistor is used to achieve
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.
Shutdown
To activate the shutdown operation, the EN/SET input for
the AAT3103-1/-2 should be pulsed low for longer than
t_OFF (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.
3103.2008.03.1.0
www.analogictech.com
11