DATA SHEET
AAT1409
Eight-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
General Description
Features
The AAT1409 is a highly integrated, high efficiency LED
backlight solution for notebook computers, monitors and
portable TVs. The device operates from DC inputs, cigarette lighter adapters, or multi-cell Li-ion batteries over
the 4.5V to 26V voltage range.
•
•
•
•
•
•
An integrated boost (step-up) converter provides up to
45V output for driving series LEDs. Eight precision current sinks are programmed up to 45mA per string
through one external RSET resistor, supporting up to 881
white LEDs at 360mA total output current.
LED strings may be disabled or operated in parallel for
increased drive capability. The boost output voltage is
set by the LED string with the highest voltage requirement, allowing a wide range of LED characteristics.
•
•
•
The PWM dimming range at 100Hz is up to 1,000:1.
The boost switching frequency is selectable (up to
1.3MHz) to allow optimum efficiency and the smallest
external L/C filtering components. Alternatively, the
device may be synchronized to an external clock.
Boost current mode control provides fast response to
line and load transients. Integrated Light-Load mode
ensures highest efficiency across the entire load range.
Fault tolerant circuitry extends system life by disabling
open LED strings. The unique high voltage current sinks
prevent damage resulting from shorted LEDs.
The AAT1409 is available in the Pb-free, thermally
enhanced 24-pin 3x4 TQFN package.
•
•
•
•
•
•
•
VIN Range: 4.5V to 5.5V / 5.0V to 26.0V
LX Rated to 50V
Maximum IOUT: 360mA
Up to 92% Efficiency
High Efficiency Light-Load Mode
8 LED Current Sinks up to 45mA/each
▪ ±2% Accuracy (21mA)
▪ ±2% Matching (21mA)
Flexible Configurations
▪ Disable or Parallel
Switching Frequency Options
▪ 675kHz or 1.3MHz
▪ Synchronize to System Clock
PWM Direct Dimming Input
▪ Up to 100kHz Prevents Audio Interference
▪ Fast Turn-On/Off
▪ Wide 1,000:1 Dimming Range (100Hz)
Fault Tolerant: Open/Short LED(s)
Current Limit Protection
Over-Voltage Protection
Over-Temperature Protection
Soft-Start Minimizes Inrush Current
TQFN34-24 Low Profile Package
-40°C to +85°C Temperature Range
Applications
• Monitors
• Notebook Computers
• Portable TV
• Portable DVD Players
• White LED Backlight
1. The maximum number of LEDs in each string is dependent upon the maximum VF of the diodes in that string. Under no event should the voltage at LX be exceeded.
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1
DATA SHEET
AAT1409
Eight-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
Typical Application
VIN: 4.5V – 26V
C1
2.2µF
50V
0805
C2
2.2µF
6.3V
0603
C3
R1
2
L1 4.7µH
R2
D1
EN
VIN
VCC
LX
COMP
RSET
FSET
VOUT: 45V at 240mA
R3
OVP
AAT1409
TQFN34-24
PWM
SYNC
Up to 88 WLED Backlight
R4
CS1
CS2
CS3
CS4
CS5
CS6
CS7
CS8
PGND GND SGND
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C4
2.2µF
50V
0805
DATA SHEET
AAT1409
Eight-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
Pin Descriptions
Pin #
Symbol
Function
1
SYNC
I
2
FSET
I
3, 4, 18, 21
GND
GND
5
PWM
I
6
7
8
9
10
11
12
13
14
15
16
CS1
CS2
CS3
CS4
SGND
CS5
CS6
CS7
CS8
RSET
COMP
O
O
O
O
GND
O
O
O
O
I
I
17
OVP
I
19
LX
O
20
PGND
GND
22
VCC
I/O
23
EN
I
24
IN
I
EP
GND
Description
Synchronizes switching frequency to external system clock. Tie to GND to disable this feature.
Connect logic high to set internal oscillator to 1300kHz. Connect logic low to set internal oscillator to 675kHz.
Connect to GND
Direct PWM input pin. Connect logic level PWM input signal in the frequency range 100Hz100kHz to this pin to enable PWM dimming.
Output current sink 1. Connect to SGND to disable channel 1.
Output current sink 2. Connect to SGND to disable channel 2.
Output current sink 3. Connect to SGND to disable channel 3.
Output current sink 4. Connect to SGND to disable channel 4.
Current sink ground tied to return of internal current sinks CS1-CS8.
Output current sink 5. Connect to SGND to disable channel 5.
Output current sink 6. Connect to SGND to disable channel 6.
Output current sink 7. Connect to SGND to disable channel 7.
Output current sink 8. Connect to SGND to disable channel 8.
Connect resistor to ground to set maximum current through the LED strings.
Connect an external resistor and capacitor to ground to compensate the boost converter.
Over-voltage protection pin. Connect resistive divider between VOUT and GND. Care should
be taken to ensure that the voltage at LX does not exceed its maximum rating under extreme
operating conditions.
Switching node of boost converter. Connect an inductor between this pin and input voltage
source. Connect the anode of Schottky diode between this pin and the boost output capacitor.
Power ground; tied to source of integrated NMOS switching device.
Internal regulated voltage when operating from input voltage range 5.0V to 26.0V. De-couple
with a 2.2µF capacitor to ground. Do not source current from this node. Input voltage pin
when operating from input voltage range 4.5V to 5.5V.
Logic high enable pin. Pull logic high or tie to IN to enable the device. Pull low to disable the
device and minimize quiescent current; pulling low also disables the internal linear regulator.
Input voltage to IC. Tied to input voltage source and input boost inductor.
Exposed paddle. Connect to PCB GND plane. PCB paddle should maintain acceptable junction
temperature.
Pin Configuration
TQFN34-24
(Top View)
PGND
GND
VCC
EN
IN
24
SYNC
FSET
GND
GND
PWM
CS1
CS2
23
22
21
20
1
19
2
18
3
17
EP
4
5
16
15
6
14
7
13
8
9
10
11
LX
GND
OVP
COMP
RSET
CS8
CS7
12
CS6
CS5
SGND
CS4
CS3
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3
DATA SHEET
AAT1409
Eight-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
Absolute Maximum Ratings1
Symbol
Description
VLX
VIN,EN
VCSx
VCC
OVP, COMP, PWM,
SYNC, RSET,
IOUT
TJ
TLEAD
PD
ΘJA
Value
LX Voltage to GND
Input Voltage, EN to GND
Output Current Sinks CS1 – CS8 to GND
VCC Voltage to GND
OVP, COMP, PWM, SYNC, CLK Voltage to GND
Maximum DC Output Current
Maximum Junction Operating temperature
Maximum Soldering Temperature (at leads, 10 sec)
Maximum Power Dissipation3
Thermal Resistance3,4
2
50
-0.3 to 30
-0.3 to 32
-0.3 to 7.0
Units
V
-0.3 to V CC + 0.3
375
-40 to +150
300
2
50
mA
W
°C/W
Value
Units
°C
Recommended Operating Conditions
Symbol
VIN
VOUT
FPWM
IOUT
TA
TJ
Description
Input Voltage Range
Output Voltage Range
PWM Dimming Frequency Range
DC Output Current
Operating Ambient Temperature
Operating Junction Temperature
5 to 26
VIN + 3 to 45
0.1 to 100
160 to 240
-40 to 85
-40 to 125
V
kHz
mA
°C
°C
1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions other than the operating conditions
specified is not implied. Only one Absolute Maximum Rating should be applied at any one time.
2. Based on long-term current density limitation.
3. Mounted on an FR4 board.
4. Derate 20mW/°C above 25°C.
4
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DATA SHEET
AAT1409
Eight-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
Electrical Characteristics1
VIN = 12V; CIN = 4.7µF, COUT = 2.2µF; CVCC = 2.2µF; L1 = 10µH; RSET =7.5kΩ (ICSx = 21mA); TA = -40oC to 85oC unless
otherwise noted. Typical values are at TA = 25oC.
Symbol
Description
Conditions
Min
Typ
Max
Units
Power Supply, Current Sinks
VIN
VUVLO
Input Voltage Range
Under Voltage Threshold
VCC
VCC Output Voltage
VCX
Current Sink Voltage
IQ
IN Quiescent Current (no switching)
ISD
IN Pin Shutdown Current
ICSx
ICSx-Matching
VOVP
RDS(ON)LO
DMAX
TMIN
ICSx / IRSET
ILIMIT
ILEAK
Current Sink Accuracy
Current Matching Between Any Sink Channel
Over-Voltage Threshold
Over-Voltage Hysteresis
Low Side Switch On Resistance
Maximum Duty Cycle
Minimum On-Time
Current Set Ratio
Low Side Switch Current Limit
LX Pin Leakage
CSx Pin Leakage
FOSC
Oscillator Frequency
FSYNC
Sync Frequency
FSYNC
Sync Duty Cycle Range
FPWM(MAX)
Maximum Direct PWM Frequency
TSS
Soft-Start Time
Logic Level Inputs: EN Pin
VEN(L)
Threshold Low
VEN(H)
Threshold High
ILEN
Input Leakage Enable Pin
Logic Level Inputs: SYNC, PWM, FSET Pins
V(H)
Threshold Low
V(H)
Threshold High
ILK
Input Leakage
TPWM(ON/OFF) PWM Turn On/Off Delay
Thermal Protection
TJ(SD)
TJ Thermal Shutdown Threshold
TJ(HYS)
TJ Thermal Shutdown Hysteresis
VIN = VCC
VCC = Open
VIN Rising
Hysteresis
VIN Falling
EN = Logic High, ICC(OUT) = 0mA
EN = Logic High, ICSx = 21mA (RSET =
7.5kΩ)
ICSx = 0% , VCSx = 0.5V, EN = Logic High
CS1-CS8 = Open, EN = Logic Low, does
not include LX leakage current
ICSx = 21mA
ICSx = 21mA
VOUT Rising
VOUT Falling
VCC = 4.5V
4.5
5.0
5.5
26.0
4.3
500
3.2
4.0
-5
-3
1.1
4.5
6
V
1.5
mA
40.0
µA
+5
+3
1.3
6.5
1
10
%
%
V
mV
mΩ
%
ns
A/A
A
µA
µA
±2
±2
1.2
100
200
100
262
3.0
EN =
EN =
FSET
VIN =
FSET
VIN =
Logic Low; VLX = 40V
Logic Low, CSx = 30V
= Logic Low; VIN = 5.0 to 26.0V;
VCC = 4.5 to 5.5V
= Logic High; VIN = 5.0 to 26.0V;
VCC = 4.5 to 5.5V
550
675
800
kHz
1100
1300
1500
kHz
FOSC
±20%
FOSC ± 20%
10
50
1
VOUT = 35V, CCOMP = 18nF, RCOMP = 10kΩ
kHz
90
100
%
kHz
ms
0.4
V
V
µA
2.5
VEN = 5V, VIN = 5V
3
0.4
VSYNC = VPWM = VFSET = 5V
PWM transition to 95%/5% IRSET
V
mV
V
V
0.5
90
ICSx/IRSET , VRSET = 0.6V
V
1
V
V
µA
µs
140
15
°C
°C
1.4
-1
1
1. The AAT1409 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured by design, characterization, and correlation with statistical process controls.
2. Output voltage must result in a voltage lower than the LX maximum rating under all operating conditions.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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5
DATA SHEET
AAT1409
Eight-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
Typical Characteristics
Boost Efficiency vs. Input Voltage
Boost Efficiency vs. Load Current
(L = 10µH; VCC = 4.7V; PWM = VCC; FSET = GND)
100
100
90
90
80
80
Efficiency (%)
Efficiency (%)
(L = 10µH; VCC = 4.7V; PWM = VCC; FSET = GND; IOUT = 360mA)
70
60
50
40
VOUT = 29V
VOUT = 36V
30
20
6
8
10
12
14
16
18
20
22
24
70
60
50
40
20
10
26
Input Voltage (V)
Total Output Current (mA)
Efficiency (%)
80
70
60
50
VIN = 9V, VOUT = 29V
VIN = 12V, VOUT = 36V
VIN = 24V, VOUT = 45V
10
20
30
40
50
60
70
80
90
100
PWM Duty Cycle (%)
255
290
80
60
40
20
0
10
20
30
40
50
60
70
80
4.7
4.6
4.6
4.4
4.55
4.2
4
4.5
4.45
3.8
4.4
3.6
4.35
85°C
25°C
-40°C
4.3
Temperature (°C)
60
100
VCC Line Regulation vs. Input Voltage
4.65
35
90
PWM Duty Cycle (%)
5
10
360
100
4.8
-15
325
120
0
VCC (V)
Current Limit (A)
220
140
(VIN = 5V to 26V)
6
185
160
Low Side Switch Current Limit vs. Temperature
3.4
-40
150
(VIN = 12V; ICSx = 20mA/ch)
90
0
115
Output Current vs. PWM Duty Cycle
100
20
80
(L = 10µH; VCC = 4.7V; FSET = GND)
30
45
Output Current (mA)
Boost Efficiency vs. PWM Duty Cycle
40
VIN = 9V, VOUT = 28V
VIN = 12V, VOUT = 36V
VIN = 24V, VOUT = 46V
30
6
85
8
10
12
14
16
18
20
Input Voltage (V)
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22
24
26
DATA SHEET
AAT1409
Eight-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
Typical Characteristics
Quiescent Current vs. Input Voltage
Shutdown Current vs. Input Voltage
(Non-switching; VCSX = 0.5V; ICSX =0mA)
(VLX = VCSX = Open)
20
Shutdown Current (µA)
Quiescent Current (mA)
1.4
1.35
1.3
1.25
1.2
1.15
1.1
85°C
25°C
-40°C
1.05
1
6
8
10
12
14
16
18
20
22
24
18
16
14
12
10
8
6
85°C
25°C
-40°C
4
2
0
26
6
8
10
Input Voltage (V)
3
1.28
2
OVP Voltage (V)
Switching Frequency Error (%)
1.3
1
0
-1
-2
FSET = GND
FSET = VCC
10
35
60
1.22
1.2
1.18
1.16
1.14
-15
35
60
85
(VIN = 12V; VCSX = 0.8V; ICSX = 21mA/Channel)
Current Sink Matching (%)
Current Sink Accuracy (%)
10
Current Sink Matching vs. Temperature
3
2
1
0
-1
-2
-3
Temperature (°C)
26
Temperature (°C)
4
35
24
1.24
1.1
-40
85
(VIN = 12V; VCSX = 0.8V; ICSX = 21mA/Channel)
10
22
1.12
Current Sink Accuracy vs. Temperature
-15
20
1.26
Temperature (°C)
-4
-40
18
(VIN = 12V)
4
-15
16
Over-Voltage Threshold vs Temperature
(VIN = 12V)
-4
-40
14
Input Voltage (V)
Switching Frequency vs. Temperature
-3
12
60
85
1.6
1.4
1.2
1
0.8
0.6
0.4
0.2
0
-40
-15
10
35
60
85
Temperature (°C)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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7
DATA SHEET
AAT1409
Eight-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
Typical Characteristics
Startup
Switching Waveforms
(VIN = 12V; VOUT = 37V; COUT = 2.2μF;
L = 4.7µH; IOUT = 160mA)
VIN
(AC coupled)
(50mV/div)
EN
(10V/div)
VOUT
(20V/div)
IOUT
(100mA/div)
(VIN = 12V; VOUT = 37V; COUT = 2.2μF;
L = 4.7µH; IOUT = 160mA)
VOUT
(AC coupled)
(200mV/div)
12V
ILX
(2A/div)
ILX
(1A/div)
Time (100µs/div)
Time (500ns/div)
PWM Switching Waveforms
(VIN = 12V; VOUT = 37V; COUT = 2.2μF;
L = 4.7µH; IOUT = 160mA)
PWM
(5V/div)
VOUT
(1V/div)
37V
IOUT
(100mA/div)
ILX
(1A/div)
Time (100µs/div)
8
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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DATA SHEET
AAT1409
Eight-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
Functional Block Diagram
IN
LX
Linear Reg
VCC
CS1
EN
OVP
CS2
CS3
VREF
COMP
SYNC
FSET
CS4
P
PWM
CS5
Logic
Osc
CS6
CS7
CS8
S
P
GND
S
PGND SGND
Functional Description
The AAT1409 is a highly integrated, high efficiency white
LED backlight solution for notebook computers, monitors
and portable TVs. The device operates from regulated
DC inputs, cigarette lighter adapters, and multi-cell
Li-ion batteries over a voltage range from 4.5V to 26V.
The integrated boost (step-up) converter provides up to
45V output to drive multiple strings of series LEDs. The
maximum number of LEDs is dependent upon the forward voltage of each LED. Eight precision current sinks
can provide constant current drive for up to 88 white
LEDs depending upon LED VF. The LED current is set by
a single external resistor up to 45mA per string for a
total output current capability of 360mA. The controller
derives output feedback from the channel with the lowest
current sink voltage while maintaining the programmed
current in each LED string. This ensures the lowest possible output voltage, highest efficiency and continuous
operation with mismatched LED strings.
RSET
The AAT1409 is designed for maximum flexibility. The LED
strings may be disabled or used in parallel for increased
current capability. Thus, the AAT1409 allows operation
with fewer than 8 LED strings with the maximum number
of LEDs per channel set by the LED VF and the output voltage of the boost converter. A lower number of LEDs can
also be used. Unused current sinks are disabled by tying
them to ground. The unique high voltage current sinks
support non-matching LED strings (LED quantity, type,
etc.). For high current applications, such as high-brightness LEDs, multiple current sinks may be connected in
parallel providing up to 360mA per LED string.
The AAT1409 supports a high input PWM frequency to
help eliminate potential audio emissions caused by harmonic/sub-harmonic resonance of the power stage. The
PWM dimming range is up to 1,000:1 (see Figure 1).
The output voltage is regulated by the string with the
highest voltage requirement, allowing a wide range of
LED characteristics. The boost switching frequency is
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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9
DATA SHEET
AAT1409
Eight-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
adjustable up to 1300kHz for optimum efficiency and the
smallest external filtering components. Alternatively, the
device may be synchronized to an external clock.
Current mode control provides fast response to line and
load transients. Integrated light load mode ensures
highest efficiency across the entire input voltage and load
range.
Fault tolerant circuitry extends system life by disabling
open LED strings. The high voltage current sinks maintain normal operation with non-matched strings while
also preventing damage due to shorted LEDs.
The AAT1409 is available in a Pb-free, thermally enhanced
24-pin 3x4mm TQFN package.
PWM Dimming
The AAT1409 provides direct PWM dimming. After initial
power-up or when EN is cycled, the device is enabled
with brightness (default) controlled by the PWM duty
cycle and the RSET resistor value.
The ultra-fast 1µs turn-on and turn-off time of the boost
regulator and current sinks ensures high performance
and excellent dimming range in applications requiring
high frequency PWM dimming. The high PWM dimming
frequency eliminates audio interference. The integrated
current sinks ensure good timing between strings (PWM
matching) while the fast response yields a linear PWM
duty-cycle versus LED current characteristic. PWM
inputs from 100Hz to 100kHz are recommended.
AAT1409 Dimming Range
vs. PWM Pin Frequency
The AAT1409 device is protected from faults arising from
LED opens and/or shorts.
An LED open condition will be detected by the controller
at startup and during normal operation. The low voltage
on the current sink is detected by the controller, which
disables the feedback to the boost converter from that
current sink. The remaining LED strings continue to
operate normally. The controller re-enables the current
sink feedback if the LED open condition is removed during a power or EN cycle. This feature extends backlight
life and reliability, which is otherwise limited by intermittent conditions in the LED string(s) and/or circuit board
interconnections.
Under all conditions, the over-voltage protection circuitry
prevents the switching node (LX) from exceeding the
maximum operating voltage prior to disabling the current
sink. Over-voltage protection (OVP) disables boost switching while maintaining the programmed LED current.
Boost switching is re-enabled when OVP hysteresis is
satisfied.
A LED short condition results in a higher voltage appearing on the affected channels' current-sink pin. The
affected current sink automatically compensates for the
additional voltage. The current sink can withstand a high
voltage indefinitely. However, the increased voltage
across the current sink causes an increase in power dissipation. The channel will continue to operate until the
over-temperature protection activates.
Integrated over-current protection is provided. Overcurrent protection prevents inductor saturation and any
resulting damage to the switching device occurring during an overload fault condition.
100000
Dimming Range
Fault Tolerant Operation
10000
1000
100
10
1
1
10
100
1000
10000
100000
PWM Frequency (Hz)
Figure 1: PWM Input Frequency
vs. Dimming Range.
10
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202118A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012
DATA SHEET
AAT1409
Eight-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
Application Information
The output voltage at the minimum OVP threshold is
OVP Protection with Open LED Failure
The OVP protection consists of a resistive divider network (R3 and R4) as shown in Figure 2. The resistor
divider must be selected so that the voltage at the OVP
pin exceeds the OVP rising threshold when the output is
at VOUT(MAX).
The maximum voltage of each LED string including the
current sink headroom should not exceed VOUT(MIN).
VOUT(MIN) > VCSX + N · VFLED(MAX)
VOUT(MAX)
-1
R3 = R4 ·
VOVP(MAX)
When the OVP rising threshold is exceeded, the converter stops switching. The open LED channel is removed
from the boost converter feedback loop. When the voltage at the OVP pin falls below the OVP hysteresis voltage, the boost converter can resume switching.
It is important that during normal operation the current
sinks are given enough headroom so that the OVP
threshold is not tripped.
VCC
R3
+1
R4
VOUT(MIN) = VOVP(MIN) ·
VOVP(MIN) ·
R3
+ 1 > VCSX + N · VFLED(MAX)
R4
R3 > R4 ·
VCSX + N · VFLED(MAX) - VOVP(MIN)
VOVP(MIN)
Where:
N is the number of LEDs in each string.
VOVP(MIN) = 1.1V is minimum over voltage threshold.
VCSX = 0.5V is the current sink voltage.
VFLED(MAX) is the maximum LED forward voltage at 20mA.
L1
D1
VOUT
VIN
C4
C1
LX
R3
VRSET = 0.6V
OVP
I R2
262 .I R2
R4
1.2V
R2
Figure 2: Over-Voltage Protection and Current Sink Setting Circuit.
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11
DATA SHEET
AAT1409
Eight-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
Another factor in setting the OVP voltage using the resistive divider is that the maximum voltage at the LX pin
does not exceed VLX(MAX) = 50V.
VLX(MAX) = VOUT(MAX) + VD1 + VRING
VD1 is the forward voltage of the Schottky diode D1
VRING is the voltage spike at the LX node caused by the
delay of D1 at turn on.
Measurements should confirm that the maximum switching node voltage VLX(MAX) is less than 50.0V under worst
case conditions.
For example, if the number of white LEDs in each string
is N =11, the resistor divider R3 can be calculated by
selecting R4 = 12.1kΩ:
R3 > 12.1kΩ ·
0.5V + 11 · 3.7V - 1.1
1.1
= 441.1kΩ
choose R3 = 442kΩ.
The maximum output voltage with the selected values of
R4, R3 is
VOUT(MAX) = VOVP(MAX) ·
R3
+ 1 = 48.8V
R4
LED Current Sink Setting
The current sink is controlled by the RSET voltage (0.6V)
and the RSET resistor (R2). For maximum accuracy, a 1%
tolerance resistor is recommended.
The RSET resistor (R2) value can be calculated as follows:
R2 =
262 · 0.6V
ICSX(MAX)
Where VRSET = 0.6V.
For example, if the maximum current for each string of
LEDs is 30mA, this corresponds to a minimum resistor
value of 5.23kΩ.
R2 =
12
Maximum ILED Current (mA)
R2 (kΩ)
45
30
25
20
15
10
5
3.48
5.23
6.19
7.87
10.5
15.8
31.6
Table 2: Maximum LED Current Sink vs. RSET
Resistor (R2) Values.
Schottky Diode Selection
To ensure minimum forward voltage drop, high voltage
Schottky diodes are considered the best choice for the
White LED boost converter. The output diode is sized to
maintain acceptable efficiency and reasonable operating
junction temperature under full load operating conditions. Forward voltage (VF) and package thermal resistance (θJA) are the dominant factors to consider in
selecting a diode. The diode non-repetitive peak forward
surge current rating (IFSM) should be considered for high
pulsed load applications. IFSM rating drops with increasing conduction period. Manufacturers’ datasheets should
be consulted to verify reliability under peak loading conditions. The diode’s published current rating may not
reflect actual operating conditions and should be used
only as a comparative measure between similarly rated
devices.
During the on-time, the output voltage on the output
cap is applied to the cathode of the external Schottky
diode. The rectifier's reverse breakdown voltage rating
should be greater than the maximum output voltage rating of the Boost. 40V rated Schottky diodes are recommended for outputs less than 30V, while 60V rated
Schottky diodes are recommended for outputs greater
than 35V.
The average diode current is equal to the output current.
IAVG = IOUT
262 · 0.6V
= 5.23kΩ
30mA
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DATA SHEET
AAT1409
Eight-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
The approximate power loss on the Schottky diode can
be determined:
PLOSS-DIODE = IAVG · VF = IOUT · VF
Diode junction temperature can be estimated.
TJ = TAMB + θJA · PLOSS-DIODE
Output diode junction temperature should be maintained
below 110°C, but may vary depending on application
and/or system guidelines. The diode θJA can be minimized
with additional PCB area on the cathode. PCB heat-sinking the anode may degrade EMI performance. The
reverse leakage current of the rectifier must be considered to maintain low quiescent (input) current and high
efficiency under light load. The rectifier reverse current
increases dramatically at elevated temperatures.
Inductor Selection
The white LED boost (step-up) converter is designed to
operate with a minimum inductor value of 4.7μH for all
input and output voltage combinations. The inductor
saturation current rating should be greater than the
NMOS current at maximum duty cycle.
DMAX =
(VOUT + VF - VIN(MIN))
VOUT + VF
The inductor (L) is selected to avoid saturation at minimum input voltage, maximum output load conditions.
Peak current may be calculated from the following equation, again assuming continuous conduction mode.
Worst-case peak current occurs at minimum input voltage (maximum duty cycle) and maximum load.
IPEAK =
IOUT
DMAX · VIN(MIN)
+
1 - DMAX
2 · FS · L
Output Capacitor
The high output ripple inherent in the boost converter
necessitates low impedance output filtering.
Multi-layer ceramic (MLC) capacitors provide small size
and adequate capacitance, low parasitic equivalent
series resistance (ESR) and equivalent series inductance
(ESL), and are well suited for use with the white LED
boost regulator. MLC capacitors of type X7R or X5R are
recommended to ensure good capacitance stability over
the full operating temperature range.
The output capacitor is sized to maintain the output load
without significant voltage droop (ΔVOUT) during the
power switch ON interval, when the output diode is not
conducting. A ceramic output capacitor from 2.2μF to
4.7μF is recommended. Typically, 50V rated capacitors
are required for the 42V maximum boost output.
Ceramic capacitors sized as small as 0805 or 1206 are
available which meet these requirements.
MLC capacitors exhibit significant capacitance reduction
with applied voltage. Output ripple measurements
should confirm that output voltage droop and operating
stability are acceptable. Voltage derating can minimize
this factor, but results may vary with package size and
among specific manufacturers.
The output capacitor size can be estimated using the
equation:
COUT =
IOUT · DMAX
FS · ∆VOUT
To maintain stable operation at full load, the output
capacitor should be sized to maintain ΔVOUT between
100mV and 200mV.
The WLED boost converter input current flows during
both ON and OFF switching intervals. The input ripple
current is less than the output ripple and, as a result,
less input capacitance is required.
Compensation Component Selection
The AAT1409 Boost architecture uses peak current mode
control to eliminate the double pole effect of the output
L&C filter and simplifies the compensation loop design.
The current mode control architecture simplifies the
transfer function of the control loop to be a one-pole,
one left plane zero and one right half plane (RHP) system
in the frequency domain. The dominant pole can be calculated by:
fP =
1
2π · R0 · C4
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13
DATA SHEET
AAT1409
Eight-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
The ESR zero of the output capacitor (see Figure 3) can
be calculated by:
fZ_ESR =
1
2π · RESR · C4
It is recommended to design the bandwidth
decade lower than the frequency of RHP zero to
tee the loop stability. A series capacitor and
network (R1 and C3) connected to the COMP pin
pole and zero which are given by:
Where:
fP_COM =
C4 is the output filter capacitor
RO is the equivalent load resistor value
RESR is the equivalent series resistance of the output
capacitor.
fZ_COM =
The right half plane (RHP) zero can be calculated by:
fZ_ESR =
VIN2
2π · L1 · IOUT · VOUT
to one
guaranresistor
sets the
1
2π · REA · C3
1
2π · R1 · C3
Where:
C3 is the compensation capacitor
R1 is the compensation resistor
REA is the output resistance of the error amplifier
(2.97MΩ).
A 15nF (C3) capacitor and a 5kΩ (R1) resistor in series
are chosen for optimum phase margin and fast transient
response.
VIN
L1
VOUT
D1
ESR
RO
I OUT
C4
Figure 3: AAT1409 Equivalent Output Stage.
14
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DATA SHEET
AAT1409
Eight-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
VIN
5V - 26V
D1
L1 4.7μH
MSS1P6
R3
442k
JP1
19
C1
10µF
35V
23
24
22
C2
2.2µF
10V
C3
15nF
5
JP4
16
R1
4.99k
JP3
R2
7.5k
2
1
OVP
PWM
COMP
17
C4
2.2µF
50V
0805
R4
12.1k
VCC
AAT1409
RSET
FSET
SYNC
6
CS1
7
CS2
8
CS3
CS4 9
CS5 11
12
CS6
13
CS7
14
CS8
EP
20
PGND
21
GND
18
GND
4
GND
3
GND
10
SGND
JP2
15
LX
EN
IN
10 LEDs in series
VOUT
U1
TQFN34-24
L1 Sumida, CDRH5D28RHPNP-4R7N, 4.7μH, 3.7A, DCR = 43.1mΩ
D1 Vishay, Schottky Barrier Diode, MSS1P6, 1A, 60V
C1 Taiyo Yuden, GMK325BJ106KN-T, 10μF, 35V, X5R,1210; OR Murata GRM32ER71H106K, 10μF, 50V, X7R, 1210
C2 2.2μF, 10V, 0603
C3 Cap, 15nF, 10V, 0603
C4 Murata, GRM31CR71H225KA88L, 2.2μF, 50V, X7R, 1206
R1, R2, R3, R4 Carbon Film resistors, 1%, 0603
Figure 4: AAT1409IMK Evaluation Board Schematic.
Figure 5: AAT1409IMK Evaluation Board
Top Side Layout.
Figure 6: AAT1409IMK Evaluation Board
Bottom Side Layout.
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15
DATA SHEET
AAT1409
Eight-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
60V or Higher Output
Voltage Applications
The maximum voltage of the LX pin cannot exceed 50V
that limits the output voltage of AAT1409 to less than
50V. For larger panel driver applications where the number of LEDs in each string exceeds the maximum LEDs
supported by the AAT1409, a high voltage external
N-Channel MOSFET Q1 is stacked to the LX pin to protect the internal low-side switch from the output voltage
greater than 50V. As illustrated in Figure 7, two
AAT1409s are connected in Master and Slave configuration in order to drive 16 parallel strings with 18 LEDs in
series for each string. The Master has a boost configuration with inductor L1, Schottky diode D1, and high voltage N-channel MOSFET Q1, while the Slave operates as
additional 8-channel current sinks. The LX pins, VOUT,
OVP pins, SYNC pins, and PWM pins of the Master and
Slave should be connected together for synchronization.
The gate of Q1 is connected to the input voltage via a
resistive divider (R9 and R10) to keep its gate to source
voltage within the maximum rating (±20V).
16
High Voltage MOSFET Selection
During the OFF-time, the energy stored in the inductor
boosts-up the Drain terminal of Q1 to VOUT + VD1. During
the ON-time, the LX node pulls-down the source terminal of Q1 to GND. Therefore, the N-channel MOSFET Q1
must have a maximum operating VDSS exceeding the
maximum output voltage (VOUT(MAX) = 60V for 18 LEDs in
series). The conduction loss (PLOSS) for a given MOSFET
RDS(ON) can be calculated in the following equation:
PLOSS = D · RDS(ON) · IL(AVG)2 +
∆IL2
12
Where:
D is the duty cycle
IL(AVG) is average inductor current
∆IL is the peak-to-peak inductor current.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202118A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012
DATA SHEET
AAT1409
Eight-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
VIN
R9
100kΩ
12V-26V
C9
2.2μF
35V
4.7μH
U1
23
EN
24
IN
VCC
C2
2.2μF
10V
C3
15nF
R1
4.99k
R2
7.5k
SYNC
R3
732k
19
LX
COMP
15
RSET
FSET
1
SYNC
5
PWM
OVP
AAT1409
PWM
17
CS1
CS2
CS3
CS4
CS5
CS6
CS7
CS8
7
8
9
11
12
13
14
7.5k
R7
732k
LX
OVP
17
18 LEDs in series
C8
2.2μF
100V
1210
R8
12.1k
COMP
15
RSET
2
20
R6
VOUT = 60V
19
EN
IN
VCC
16
4.99k
21
C5
10μF
35V
R5
18
22
C7
C6
2.2μF
15nF
10V
4
3
10
24
C4
2.2μF
100V
1210
6
EP
PGND
GND
GND
GND
GND
SGND
U2
23
18 LEDs in series
R4
12.1k
16
2
VOUT = 60V
SS38
Q1
SI4480DY
R10
200kΩ
22
C1
10μF
35V
D1
L1
AAT1409
FSET
5
PWM
1
SYNC
6
7
8
9
11
12
13
14
EP
PGND
GND
GND
GND
GND
SGND
CS1
CS2
CS3
CS4
CS5
CS6
CS7
CS8
20
21
4
18
3
10
Q1: Fairchild, FDD86102, N-Channel, 8A, VDS = 100V, D-PAK
L1: Cooper Bussmann, DR1050-4R7-R, 4.7μH, 6.7A, DCR = 11.9mΩ
D1: Fairchild, Schottky Barrier Diode, SS38, 3A, 80V
C1, C5: Taiyo Yuden, GMK325BJ106KN-T, 10μF, 35V, X5R, 1210; OR Murata GRM32ER71H106K, 10μF, 50V, X7R, 1210
C2, C6: 2.2μF, 10V, 0603
C3, C7: Cap, 15nF, 10V, 0603
C4, C8: Murata, GRM32ER72A225KA35L, 2.2μF, 100V, X7R, 1210
Figure 7: Application Schematic For 60V/320mA Output, 288LEDs Using Master and Slave Configuration.
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17
DATA SHEET
AAT1409
Eight-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
Ordering Information
Package
Marking1
Part Number (Tape and Reel)2
TQFN34-24
D1XYY
AAT1409IMK-T1
Skyworks Green™ products are compliant with
all applicable legislation and are halogen-free.
For additional information, refer to Skyworks
Definition of Green™, document number
SQ04-0074.
Package Information
TQFN34-243
3.000 ± 0.050
1.700 ± 0.050
Index Area
0.400 ± 0.050
R(5x)
2.700 ± 0.050
4.000 ± 0.050
0.210 ± 0.040
0.400 BSC
Detail “A”
Bottom View
Detail “A”
0.750 ± 0.050
Top View
0
+ 0.10
- 0.00
0.203 REF
Side View
All dimensions in millimeters.
1. XYY = assembly and date code.
2. Sample stock is generally held on part numbers listed in BOLD.
3. The leadless package family, which includes QFN, TQFN, DFN, TDFN and STDFN, has exposed copper (unplated) at the end of the lead terminals due to the manufacturing
process. A solder fillet at the exposed copper edge cannot be guaranteed and is not required to ensure a proper bottom solder connection.
18
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202118A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012
DATA SHEET
AAT1409
Eight-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
Copyright © 2012 Skyworks Solutions, Inc. All Rights Reserved.
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responsibility whatsoever for conflicts, incompatibilities, or other difficulties arising from any future changes.
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THE MATERIALS, PRODUCTS AND INFORMATION ARE PROVIDED “AS IS” WITHOUT WARRANTY OF ANY KIND, WHETHER EXPRESS, IMPLIED, STATUTORY, OR OTHERWISE, INCLUDING FITNESS FOR A PARTICULAR
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Customers are responsible for their products and applications using Skyworks products, which may deviate from published specifications as a result of design defects, errors, or operation of products outside of published parameters or design specifications. Customers should include design and operating safeguards to minimize these and other risks. Skyworks assumes no liability for applications assistance, customer product
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