AAT3164 Datasheet, PDF (10/14 Pages) Advanced Analogic Technologies – High Efficiency 1X/1.5X/2X Charge Pump for Six-Channel White LED Applications

AAT3164
High Efficiency 1X/1.5X/2X Charge Pump for
Six-Channel White LED Applications
Applications Information
LED Selection
Although the AAT3164 is specifically designed to
drive white LEDs, the device can also be used to
drive most types of LEDs with forward voltage
specifications ranging from 2.0V to 4.7V. LED
applications may include LCD display backlight-
ing, camera photo-flash applications, color (RGB)
LEDs, infrared (IR) diodes for remotes, and other
loads benefiting from a controlled output current
generated from a varying input voltage. Since the
D1 to D6 input current sinks are matched with
negligible voltage dependence, the LED bright-
ness will be matched regardless of the specific
LED forward voltage (V_F) levels. In some
instances (e.g., in high luminous output applica-
tions such as photo flash), it may be necessary to
drive high-V_F type LEDs. The low dropout (~0.1V
@ 20mA I_LED) current sinks in the AAT3164 make
it capable of driving LEDs with forward voltages
as high as 4.7V from an input supply as low as
3.0V. Outputs can be paralleled to drive high-cur-
rent LEDs without complication.
Determining the Maximum LED Current
Level
The value of R_SET determines the maximum LED
current level. In the typical application, selecting
R_SET = 26.1kΩ results in 20mA/channel LED cur-
rent. From this reference point, the R_SET value
required for other current levels can be calculated
as:
20mA · 26.1kΩ
R_SET =
I_LED(MAX)
A visual representation of the maximum LED cur-
rent per channel versus R_SET value is shown in
Figure 2.
45
40
35
30
25
20
15
10
5
0
10 15 20 25 30 35 40 45 50 55 60 65 70 75
R_SET (kΩ)
Figure 2: Maximum LED Current vs. R_SET.
Brightness Control Using the RSET Pin
Additional methods of brightness control can be
achieved with the RSET pin. For example, using an
additional resistor to connect the RSET pin with a
digital output provides a HI/LO control. Figure 3
illustrates a configuration of the RSET pin utilizing
two resistors.
HI/LO
or
V_DAC
R2
R₁
AAT 3164
RSET
Figure 3: RSET Configuration Using
Two Resistors.
When the digital output is asserted high, the result-
ing brightness level is LO and the individual LED
currents are:
I_LED(LO)
=
870
⎛ 0.6
⎝R₁ // R₂
-
V_IO⎞
R₂ ⎠
When the digital output is asserted low, the result-
ing brightness level is HI and the individual LED
currents are:
I_LED(HI)
=
870
⎛ 0.6 ⎞
⎝R₁ // R₂⎠
10
3164.2006.07.1.0