AAT2400 Datasheet, PDF (21/32 Pages) Skyworks Solutions Inc. – Sixteen-Channel White LED Driver Solution

DATA SHEET
AAT2400/2401
Sixteen-Channel White LED Driver Solution
with Full LED Current and Timing Control
Application Information
Channel Disable
If current sink channels on either the AAT2400 or AAT2401
are not used, they must be terminated. Unused channels
should have their corresponding bit in the CTL1 or CTL2
register set to zero. In applications where the AAT2400/
AAT2401 pair are used, unused channels may be tied to
GND or to VCC. In applications where the AAT2401 is
used alone, unused channels must be tied to VCC.
LED Selection
Although the AAT2400 and 2401 are specifically designed
to drive high current white LEDs, the device can also be
used to drive most types of LEDs with forward voltages
ranging between 2.0V and 4.7V. Since all current sinks
are matched with low voltage dependence, the LED-to-
LED brightness will be matched regardless of the indi-
vidual LED forward voltage (V_F) levels. It makes the
AAT2400 and 2401 a perfect combination for large LCD
TV backlighting LED applications.
prevents damage to the device when one of the 16 chan-
nels has an open LED circuit. The rest of the channels of
AAT2400 and AAT2401 continue to operate.
The resistor divider can be selected such that the over-
voltage threshold occurs prior to the output reaching 45V
(V_OUT(MAX)). The value of R5 should be selected from 10kΩ
to 20kΩ to minimize switching losses without degrading
noise immunity.
R₄ = R₅
V_{OUT(PROTECTION)}
V_OVP
-
1
AAT2400
OVP
AGND
VOUT
R4
R5
COUT
Constant Current Setting
The LED current is controlled by the R_SET resistor. For
maximum accuracy, a 1% tolerance resistor is recom-
mended. Table 21 shows the R_SET resistor value for
AAT2400 and 2401 for various LED full-scale current
levels.
R_SET
=
1024(A/A)
I_CSx
·
0.6V
I_CSX (mA)
40
50
60
70
80
90
100
R_SET (kΩ)
15.4
12.3
10.2
8.76
7.68
6.81
6.12
Table 21: Maximum LED Current and R_SET
Resistor Values (1% Resistor Tolerance).
Over-Voltage Protection
The over-voltage protection circuit consists of a resistor
network connected from the output voltage to the OVP
pin (see Figure 2). This over voltage protection circuit
Figure 2: Over-Voltage Protection Circuit.
If 10 LEDs are connected in series on one channel sink,
the total V_F from the WLEDs could be as high as 42V.
Therefore, using R5 = 12.1kΩ and setting V_{OUT(PROTECTION)} =
45V is recommended. Selecting a 1% resistor, this results
in R4 = 442kΩ (rounded to the nearest standard 1%
value). It is always recommended to use the same num-
ber of WLEDs on each channel and set the appropriate
over-voltage protection. Failure to do so may cause any
one of the 16 sink pins to exceed the absolute maximum
rating voltage and permanently damage the device in
case the channel is disconnected (open circuit failure).
LED Brightness Control
The AAT2400 and 2401 uses the SPI interface to program
and control LED brightness. Each channel sink current of
the AAT2400 and AAT2401 can be changed successively
to brighten or dim the LED string in smooth transitions
(i.e. dynamic local dimming or zone dimming), giving the
user complete programmability and real-time control of
LED brightness to tune the picture background to a true-
black and a true-white from the LED technology.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [e-mail] • www.skyworksinc.com
202307A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 24, 2012
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