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PDF AAT2404 Data sheet ( Hoja de datos )
| Número de pieza | AAT2404 | |
| Descripción | Voltage-Variable Current Sourcing Boost Controller | |
| Fabricantes | Skyworks Solutions | |
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DATA SHEET
AAT2404
Voltage-Variable Current Sourcing Boost Controller For LED Lighting Applications
General Description
The AAT2404 is a highly integrated high-efficiency vari-
able voltage current sourcing boost controller for white
LED backlight applications intended for use in large size
LCD panels and LCD TVs. To accommodate various LED
backlighting configurations in both direct and edge light-
ing applications, the device uses a high voltage external
power MOSFET. The AAT2404 contains an integrated cur-
rent sense architecture eliminating the need for an
expensive low resistance/high accuracy sense resistor.
The device operates ideally from a regulated 12V or 24V
DC power supply, but can also operate over a 10.8V to
28V range.
The AAT2404 provides an output voltage up to 100V
regulated by the CSFB pin provided by the ICs in
Skyworks' family of white LED drivers for TV applications.
The CSFB pin is an analog voltage representing the LED
string with the highest voltage requirement. Regulating to
this voltage allows for a wide range of LED characteristics,
while maintaining the lowest possible power dissipation.
The CSFB regulation point can be set by adjusting a resis-
tor to ground from the RSET pin.
The boost switching frequency is nominally 400kHz to
allow for optimum efficiency with the smallest external
filter. However, the device switching frequency may be
adjusted with an external resistor to optimize system
performance. Current mode control provides fast response
to line and load transients.
Thermal protection circuitry shuts down the boost con-
verter in the event of an over-temperature condition.
The AAT2404 is available in the Pb-free, thermally
enhanced 24-pin 3 x 4mm TQFN package.
Features
• VIN Range: 10.8V – 28.0V
• Maximum VLED: 100V
• Up to 95% Boost Conversion Efficiency
• Integrated Current Sense Eliminates Need for Ballast
Resistors
• Switching Frequency Options
▪ 400KHz Nominal
▪ Adjustable Range from 100kHz to 800kHz
• Adjustable Regulation Voltage
▪ Analog Input from LED Driver
▪ User Adjustable for Fixed Output
• Integrated Low Impedance Gate Drive = VCC
• Flexible Current Sense Feedback Control
• Power OK Output
• Integrated Over-Voltage Protection
• Soft-Start to Minimize Inrush Current
• TQFN34-24 Low Profile Package
• -40°C to +85°C Temperature Range
Applications
• Large Size LCD TV, Panels
• LCD Monitors
• Video Walls
• White LED Backlighting
Typical Application
VIN = 10.8V to 28V
CIN
CVCC
D1
L1 Q1
VIN GATE LXS OVP
VCC
AAT2404
R1
R2
VLED
COUT
On/Off Enable Input
CC
RC
RFREQ
RSET
EN
COMP
POK
FREQ
RSET
CSFB
PGND AGND
Power OK Output
Current Sense Feedback Input
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202247A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 7, 2012
1
1 page  
DATA SHEET
AAT2404
Voltage-Variable Current Sourcing Boost Controller For LED Lighting Applications
Typical Characteristics
UVLO vs. Temperature
9.8
9.6
9.4
9.2
9.0
8.8
8.6
8.4
8.2
-40
Rising
Falling
-15 10 35 60
Temperature (°C)
85
Quiescent Current vs. Temperature
(VIN = 24V; VEN = VIN; Non-switching)
1.4
1.3
1.2
1.1
1.0
0.9
0.8
0.7
0.6
-40
-15
10
35 60
85
Temperature (°C)
Shutdown Current vs. Temperature
(VIN = 24V; VEN = GND)
16
14
12
10
8
6
4
2
0
-40 -15 10 35 60 85
Temperature (°C)
Efficiency vs. Load Current
(VIN = 24V; VLED = 31V; COUT = 20µF; L = 10µH)
100
96
92
88
84
80
76
72
68
0 0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6 4.0
Output Current (A)
Input Logic Threshold vs. Temperature
(VIN = 24V)
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1.0
0.9
-40
-15
10
Logic Threshold High
Logic Threshold Low
35 60 85
Temperature (°C)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202247A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 7, 2012
5
5 Page 
DATA SHEET
AAT2404
Voltage-Variable Current Sourcing Boost Controller For LED Lighting Applications
Application Information
The AAT2404 is a highly integrated high-efficiency vari-
able voltage current sourcing boost controller and like all
boost controllers care must be taken in the selection of
external components during the design stage to ensure a
stable and reliable system. The design is an iterative pro-
cess since design parameters are mutually dependant. As
an example of this iterative process please refer to the
step-by-step design example application note.
DC-DC Boost Duty Cycle Calculation
In order to correctly determine the characteristics for
external component selection, the switching duty cycle
for the boost converter function should be calculated. If
the input voltage to the AAT2404 is constant, then there
is only one maximum duty cycle condition to be con-
cerned with (Equation 3). In the case of varied input
supply, the minimum, maximum, and nominal duty cycle
should be calculated (Equations 3, 4, and 5) and the use
of the maximum value should be carried forward for the
selection of the inductor, N-channel MOSFET, and reverse
blocking diode.
Eq.
3:
DNOM
=
VLED - VIN(NOM) +
VLED + VD
VD
Eq.
4:
DMIN
=
VLED - VIN(MAX) +
VLED + VD
VD
Where:
Eq.
5:
DMAX
=
VLED - VIN(MIN) +
VLED + VD
VD
DMIN = Minimum boost switching duty cycle
DMAX = Maximum boost switching duty cycle
(must be ≤ 80%)
DNOM = nominal boost switching duty cycle
VIN[MAX] = Maximum input supply voltage for the
application
VIN[MIN] = Minimum input supply voltage for the
application
VLED = Voltage output of the boost regulator (estimate
the maximum summed VF for the LED string for the
backlighting application)
VD = Reverse blocking diode forward voltage. A
Schottky diode is recommended for this application due
to their low forward voltage characteristic. The VF of a
Schottky diode is typically between 0.5V and 0.7V.
Selecting the Switching Frequency
Selecting the optimal switching frequency is an iterative
process since component and electrical parameters are
all interrelated. For example, to reduce the inductor
value and hence its size a higher switching frequency is
desired. However, too high of a switching frequency may
cause the switching losses in the external N-channel
boost MOSFET to become dominant and exceed the
power dissipation. A good starting point for the switch-
ing frequency is between 200kHz and 400kHZ. To set
the switching frequency, please refer to the Boost
Converter Switching Frequency section of this product
datasheet.
Selecting the Boost Inductor
The first parameter to be considered in the selection of
the boost inductor is the inductance value. In a fixed-
frequency boost converter like the AAT2404, this value is
based on the desired peak-to-peak ripple current ∆IL,
which flows in the inductor along with the average or DC
inductor current IL. In continuous conduction mode (CCM)
IL is greater than the current output of the boost regula-
tor, ILED. Taking into account the conservation of power
and neglecting efficiency losses, the two currents are
related by the following:
Conservation of power:
Eq. 6: VIN · IL = VLED · ILED
Eq.
7:
VLED
=
VIN
(1 - D)
Rearranging for IL:
Eq.
8:
IL
=
VLED · ILED
VIN
Substituting VIN for VLED:
Eq. 9: IL =
VIN
(1 - D)
·
ILED
VIN
Eq.
10:
IL
=
ILED
(1 - D)
Where:
VIN = Input supply voltage
VLED = Voltage output of the boost regulator
IL = Average inductor current or input supply current
ILED = Current output of the boost regulator
D = Boost switching duty cycle
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202247A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • August 7, 2012
11
11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet AAT2404.PDF ] | |
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