AAT3192 Datasheet, PDF (12/17 Pages) Advanced Analogic Technologies – Low-Cost, 2-/3-Channel Charge-Pump LED Drivers

EN/PWM
Duty Cycle
100%
90%
80%
70%
60%
50%
40%
30%
20%
10%
D1-D3
Current (mA)
20
17.9
15.9
14
12.1
10.1
8.2
6.3
4.3
2.4
Table 4: AAT3192/93-4 LED Current Settings
20.00
15.00
10.00
5.00
0.00
100% 90% 80% 70% 60% 50% 40% 30% 20% 10%
EN/PWM Input Pin Duty Cycle (%)
Figure 5: AAT3192/93-4 Current Control Profile
12
AAT3192/93
Low-Cost, 2-/3-Channel
Charge-Pump LED Drivers
Applications Information
LED Selection
The AAT3192/93 is specifically intended for driving
white LEDs. However, the device design will allow
the AAT3192/93 to drive most types of LEDs with
forward voltage specifications ranging from 2.2V to
4.7V. LED applications may include mixed arrange-
ments for display backlighting, keypad display, and
any other application needing a constant current
sink generated from a varying input voltage. Since
the D1 to D3 constant current sinks are matched
with negligible supply voltage dependence, the
constant current channels will be matched regard-
less of the specific LED forward voltage (V_F) levels.
The low dropout current sinks in the AAT3192/93
maximize performance and make it capable of driv-
ing LEDs with high forward voltages. Multiple chan-
nels can be combined to obtain a higher LED drive
current without complication.
Constant Current Setting
The LED current is controlled by the R_SET resistor.
For maximum accuracy, a 1% tolerance resistor is
recommended. Table 5 shows the R_SET resistor value
for AAT3193-1/2/4 for various LED full-scale current
levels.
I_LED (mA)
30
20
15
10
R_SET (KΩ)
9.53
14.3
19.1
28.7
Table 5: Maximum LED Current and R_SET
Resistor Values (1% Resistor Tolerance)
for the AAT3193-1/2/4.
Device Switching Noise Performance
The AAT3192/93 operates at a fixed frequency of
approximately 1MHz to control noise and limit har-
monics that can interfere with the RF operation of
mobile communication 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
white LED backlight solutions. The AAT3192/93
soft-start feature prevents noise transient effects
3193.2007.05.1.0