AAT1405
DATA SHEET
Four-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
1
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202116A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012
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.
General Description
The AAT1405 is a highly integrated, high efficiency LED
backlight solution for notebook computers, monitors and
portable TVs. The device operates from DC inputs, ciga-
rette 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. Four precision cur-
rent sinks are programmed up to 30mA per string
through one external RSET resistor, supporting up to 441
white LEDs at 120mA 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 require-
ment, 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 AAT1405 is available in the Pb-free, thermally
enhanced 24-pin 3x4 TQFN package.
Features
•VIN Range: 4.5V to 5.5V / 5.0V to 26.0V
•LX Rated to 50V
•Maximum IOUT: 120mA
•Up to 92% Efficiency
•High Efficiency Light-Load Mode
•4 LED Current Sinks up to 30mA/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
AAT1405
DATA SHEET
Four-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
2Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202116A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012
Typical Application
LX
R4
OVP
D1 Up to 44 WLED Backlight
AAT1405
TQFN34-24
R1
C3
R3
CS1
CS2
CS3
CS4
COMP
SYNC
PGND SGND
RSET
VIN
VCC
GND
FSET
EN
PWM
R2
C1
2.2µF
50V
0805
C2
2.2µF
6.3V
0603
C4
2.2µF
50V
0805
V
OUT
: 45V at 120mA
V
IN
: 4.5V – 26V L1 4.7µH
AAT1405
DATA SHEET
Four-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
3
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202116A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012
Pin Descriptions
Pin # Symbol Function Description
1SYNC ISynchronizes switching frequency to external system clock. Tie to GND to disable this feature.
2FSET IConnect logic high to set internal oscillator to 1300kHz. Connect logic low to set internal oscillator
to 675kHz.
3, 4, 8, 9, 13,
14, 18, 21 GND GND Connect to GND.
5PWM IDirect PWM input pin. Connect logic level PWM input signal in the frequency range 100Hz-100kHz
to this pin to enable PWM dimming.
6CS1 OOutput current sink 1. Connect to SGND to disable channel 1.
7CS2 OOutput current sink 2. Connect to SGND to disable channel 2.
10 SGND GND Current sink ground tied to return of internal current sinks CS1-CS4.
11 CS3 OOutput current sink 3. Connect to SGND to disable channel 3.
12 CS4 OOutput current sink 4. Connect to SGND to disable channel 4.
15 RSET IConnect resistor to ground to set maximum current through the LED strings.
16 COMP IConnect an external resistor and capacitor to ground to compensate the boost converter.
17 OVP I
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 oper-
ating conditions.
19 LX OSwitching 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.
20 PGND GND Power ground; tied to source of integrated NMOS switching device.
22 VCC I/O
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.
23 EN ILogic 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.
24 IN IInput voltage to IC. Tied to input voltage source and input boost inductor.
EP GND Exposed paddle. Connect to PCB GND plane. PCB paddle should maintain acceptable junction
temperature.
Pin Configuration
TQFN34-24
(Top View)
1
2
3
4
5
6
EP
7
8
9
24 23 22 21 20
10 11 12
19
18
17
16
15
14
13
SYNC
FSET
GND
GND
PWM
CS1
CS2
GND
GND
SGND
CS3
CS4
COMP
OVP
RSET
GND
GND
GND
LX
PGND
GND
VCC
EN
IN
AAT1405
DATA SHEET
Four-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
4Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202116A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012
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.
Absolute Maximum Ratings1
Symbol Description Value Units
VLX LX Voltage to GND 50
V
VIN,EN Input Voltage, EN to GND -0.3 to 30
VCSx Output Current Sinks CS1 – CS4 to GND -0.3 to 32
VCC VCC Voltage to GND -0.3 to 7.0
OVP, COMP, PWM,
SYNC, RSET, OVP, COMP, PWM, SYNC, CLK Voltage to GND -0.3 to VCC + 0.3
IOUT Maximum DC Output Current2134 mA
TJMaximum Junction Operating Temperature -40 to +150 °C
TLEAD Maximum Soldering Temperature (at leads, 10 sec.) 300
PDMaximum Power Dissipation32 W
ΘJA Thermal Resistance3, 4 50 °C/W
Recommended Operating Conditions
Symbol Description Value Units
VIN Input Voltage Range 5 to 26 V
VOUT Output Voltage Range VIN + 3 to 45
FPWM PWM Dimming Frequency Range 0.1 to 100 kHz
IOUT DC Output Current 80 to 120 mA
TAOperating Ambient Temperature -40 to 85 °C
TJOperating Junction Temperature -40 to 125
AAT1405
DATA SHEET
Four-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
5
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202116A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012
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 Input Voltage Range VIN = VCC 4.5 5.5 V
VCC = Open 5.0 26.0
VUVLO Under-Voltage Threshold
VIN Rising 4.3 V
Hysteresis 500 mV
VIN Falling 3.2 V
VCC VCC Output Voltage EN = Logic High, ICC(OUT) = 0mA 4.0 4.5 6 V
VCX Current Sink Voltage EN = Logic High, ICSx = 21mA
(RSET = 7.5kΩ) 0.5 V
IQIN Quiescent Current (no switching) ICSx = 0%, VCSx = 0.5V, EN = Logic High 1.5 mA
ISD IN Pin Shutdown Current CS1-CS4 = Open, EN = Logic Low,
does not include LX leakage current 40.0 µA
ICSx Current Sink Accuracy ICSx = 21mA -5 ±2 +5 %
ICSx-Matching
Current Matching Between Any Sink Chan-
nel ICSx = 21mA -3 ±2 +3 %
VOVP
Over-Voltage Threshold VOUT Rising 1.1 1.2 1.3 V
Over-Voltage Hysteresis VOUT Falling 100 mV
RDS(ON)LO Low Side Switch On Resistance VCC = 4.5V 200 mΩ
DMAX Maximum Duty Cycle 90 %
TMIN Minimum On-Time 100 ns
ICSx/IRSET Current Set Ratio ICSx/IRSET
, VRSET = 0.6V 262 A/A
ILIMIT Low Side Switch Current Limit 3.0 6.5 A
ILEAK
LX Pin Leakage EN = Logic Low; VLX = 40V 1 µA
CSx Pin Leakage EN = Logic Low; CSx = 30V 10 µA
FOSC Oscillator Frequency
FSET = Logic Low; VIN = 5.0 to 26.0V;
VIN = VCC = 4.5 to 5.5V 550 675 800 kHz
FSET = Logic High; VIN = 5.0 to 26.0V;
VIN = VCC = 4.5 to 5.5V 1100 1300 1500 kHz
FSYNC Sync Frequency FOSC
±20% kHz
FSYNC Sync Duty Cycle Range FOSC ± 20% 10 90 %
FPWM(MAX) Maximum Direct PWM Frequency 50 100 kHz
TSS Soft-Start Time VOUT = 35V, CCOMP = 18nF, RCOMP = 10kΩ 1 ms
Logic Level Inputs: EN Pin
VEN(L) Threshold Low 0.4 V
VEN(H) Threshold High 2.5 V
ILEN Input Leakage Enable Pin VEN = 5V, VIN = 5V 3 µA
Logic Level Inputs: SYNC, PWM, FSET Pins
V(H) Threshold Low 0.4 V
V(H) Threshold High 1.4 V
ILK Input Leakage VSYNC = VPWM = VFSET = 5V -1 1 µA
TPWM(ON/OFF) PWM Turn On/Off Delay PWM transition to 95%/5% IRSET 1 µs
Thermal Protection
TJ(SD) TJ Thermal Shutdown Threshold 140 °C
TJ(HYS) TJ Thermal Shutdown Hysteresis 15 °C
1. The AAT1405 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured by design, characterization, and correla-
tion with statistical process controls.
2. Output voltage must result in a voltage lower than the LX maximum rating under all operating conditions.
AAT1405
DATA SHEET
Four-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
6Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202116A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012
Typical Characteristics
Boost Efficiency vs. Input Voltage
(L = 10µH; VCC = 4.7V; PWM = VCC; FSET = GND; IOUT = 120mA)
Input Voltage (V)
Efficiency (%)
61014182
22
6812162024
20
30
40
50
60
70
80
90
100
VOUT = 29V
VOUT = 36V
Boost Efficiency vs. Load Current
(L = 10µH; VCC = 4.7V; PWM = VCC; FSET = GND)
Output Current (mA)
Efficiency (%)
60 100 140 18040 80 120 160
20
30
40
50
60
70
80
90
100
VIN = 9V, VOUT = 28V
VIN = 12V, VOUT = 36V
VIN = 24V, VOUT = 46V
Boost Efficiency vs. PWM Duty Cycle
(L = 10µH; VCC = 4.7V; FSET = GND)
PWM Duty Cycle (%)
Efficiency (%)
020406080 10010 30 50 70 90
20
30
40
50
60
70
80
90
100
VIN = 9V, VOUT = 29V
VIN = 12V, VOUT = 36V
VIN = 24V, VOUT = 45V
Output Current vs. PWM Duty Cycle
(VIN = 12V; ICSX = 20mA/ch)
PWM Duty Cycle (%)
Total Output Current (mA)
020406080 100
0
10
20
30
40
50
60
70
80
Low Side Switch Current Limit vs. Temperature
(VIN = 5V to 26V)
Temperature (°C)
Current Limit (A)
-40-15 10 35 60 85
3.4
3.6
3.8
4
4.2
4.4
4.6
4.8
5
V
CC
Line Regulation vs. Input Voltage
Input Voltage (V)
V
CC
(V)
611162
12
6
4.3
4.35
4.4
4.45
4.5
4.55
4.6
4.65
4.7
85°C
25°C
-40°C
AAT1405
DATA SHEET
Four-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
7
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202116A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012
Typical Characteristics
Quiescent Current vs. Input Voltage
(Non-switching; VCSX = 0.5V; ICSX = 0mA)
Input Voltage (V)
Quiescent Current (mA)
61
8912152124
1
1.05
1.1
1.15
1.2
1.25
1.3
1.35
1.4
85°C
25°C
-40°C
Shutdown Current vs. Input Voltage
(VLX = VCSX = Open)
Input Voltage (V)
Shutdown Current (µA)
61014182
22
6
0
2
4
6
8
10
12
14
16
18
20
85°C
25°C
-40°C
Switching Frequency vs. Temperature
(VIN = 12V)
Temperature (°C)
Switching Frequency Error (%)
-40-15 10 35 60 85
-4
-3
-2
-1
0
1
2
3
4
FSET = GND
FSET = VCC
Over-Voltage Threshold vs Temperature
(VIN = 12V)
Temperature (°C)
OVP Voltage (V)
-40-15 10 35 60 85
1.1
1.12
1.14
1.16
1.18
1.2
1.22
1.24
1.26
1.28
1.3
Current Sink Accuracy vs. Temperature
(VIN = 12V; VCSX = 0.8V; ICSX = 21mA/Channel)
Temperature (°C)
Current Sink Accuracy (%)
-40-15 10 35 60 85
-4
-3
-2
-1
0
1
2
3
4
Current Sink Matching vs. Temperature
(VIN = 12V; VCSX = 0.8V; ICSX = 21mA/Channel)
Temperature (°C)
Current Sink Matching (%)
-40-15 10 35 60 85
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
AAT1405
DATA SHEET
Four-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
8Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202116A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012
Typical Characteristics
Startup
(VIN = 12V; VOUT = 37V; COUT = 2.2μF;
L = 4.7µH; IOUT = 80mA)
Time (100µs/div)
EN/SET
(10V/div)
VOUT
(20V/div)
IOUT
(50mA/div)
ILX
(1A/div)
12V
Switching Waveforms
(VIN = 12V; VOUT = 37V; COUT = 2.2μF;
L = 4.7µH; IOUT = 80mA)
Time (500ns/div)
VOUT
(AC coupled)
(200mV/div)
VIN
(AC coupled)
(50mV/div)
ILX
(1A/div)
PWM Switching Waveforms
(VIN = 12V; VOUT = 37V; COUT = 2.2μF;
L = 4.7µH; IOUT = 80mA)
Time (100µs/div)
IOUT
(50mA/div)
VOUT
(1V/div)
PWM
(5V/div)
ILX
(1A/div)
37V
AAT1405
DATA SHEET
Four-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
9
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202116A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012
Functional Description
The AAT1405 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 for-
ward voltage of each LED. Four precision current sinks
can provide constant current drive for up to 44 white
LEDs depending upon LED VF
. The LED current is set by
a single external resistor up to 30mA per string for a
total output current capability of 120mA. 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 pos-
sible output voltage, highest efficiency and continuous
operation with mismatched LED strings.
The AAT1405 is designed for maximum flexibility. The
LED strings may be disabled or used in parallel for
increased current capability. Thus, the AAT1405 allows
operation with fewer than 4 LED strings with the maxi-
mum 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 dis-
abled 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 120mA per LED
string.
The AAT1405 supports a high input PWM frequency to
help eliminate potential audio emissions caused by har-
monic/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
adjustable up to 1300kHz for optimum efficiency and the
smallest external filtering components. Alternatively, the
device may be synchronized to an external clock.
Functional Block Diagram
Logic
LXIN
VCC Linear Reg
EN
SYNC
CS2
CS1
RSET
GND PGND
CS3
CS4
OVP VREF
COMP
PWM
SGND
P
P
S
S
Osc
FSET
AAT1405
DATA SHEET
Four-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
10 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202116A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012
Current mode control provides fast response to line and
load transients. Integrated light load mode ensures high-
est 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 main-
tain normal operation with non-matched strings while
also preventing damage due to shorted LEDs.
The AAT1405 is available in a Pb-free, thermally enhanced
24-pin 3x4 TQFN package.
PWM Dimming
The AAT1405 provides direct PWM dimming. After initial
power-up or when EN is cycled, the device is enabled
with brightness controlled by 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.
AAT1405 Dimming Range
vs. PWM Pin Frequency
PWM Frequency (Hz)
Dimming Range
110 100 1000 10000 100000
1
10
100
1000
10000
100000
Figure 1: PWM Input Frequency
vs. Dimming Range.
Fault Tolerant Operation
The AAT1405 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 to continue to
operate normally. The controller re-enables the current
sink feedback if the LED open condition is removed dur-
ing a power or EN cycle. This feature extends backlight
life and reliability, which is otherwise limited by intermit-
tent 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 switch-
ing 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 appear-
ing 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-tem-
perature protection activates.
Integrated over-current protection is provided. Over-
current protection prevents inductor saturation and any
resulting damage to the switching device occurring dur-
ing an overload fault condition.
AAT1405
DATA SHEET
Four-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
11
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202116A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012
LX
OVP
R2
C1C4
D1
L1
R3
R4
1.2V
VIN
VOUT
VCC
VRSET
IR2
264.IR2
= 0.6V
Figure 2: Over-Voltage Protection and Current Sink Setting Circuit.
Application Information
OVP Protection with Open LED Failure
The AAT1405's 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).
R3 = R4 · - 1
V
OUT(MAX)
VOVP(MAX)
When the OVP rising threshold is exceeded, the con-
verter stops switching. The open LED channel is removed
from the boost converter feedback loop. When the volt-
age at the OVP pin falls below the OVP hysteresis volt-
age, 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.
The output voltage at the minimum OVP threshold is
VOUT(MIN) = VOVP(MIN) · + 1
R
3
R4
The maximum voltage of each LED string including the
current sink headroom should not exceed VOUT(MIN).
V
OUT(MIN)
> V
CSX
+ N · V
FLED(MAX)
VOVP(MIN) · + 1
R
3
R4
> VCSX + N · VFLED(MAX)
R3 > R4 ·
V
CSX
+ N · V
FLED(MAX)
- V
OVP(MIN)
VOVP(MIN)
Where:
N is the number of LED in each string.
VOVP(MIN) = 1.1V is the minimum over-voltage threshold.
VCSX = 0.5V is the current sink voltage.
VFLED(MAX) is the maximum forward LED voltage at 20mA.
Another factor in setting the OVP voltage using the resis-
tive divider is that the maximum voltage at the LX pin
should not exceed VLX(MAX) = 50V.
V
LX(MAX)
= V
OUT(MAX)
+ V
D1
+ V
RING
VD1 is the forward voltage of the Schottky diode D1.
VRING is the voltage spike at LX node caused by the delay
of D1 at turn on.
Measurements should confirm that the maximum switch-
ing node voltage VLX(MAX) is less than 50V under worst case
conditions.
AAT1405
DATA SHEET
Four-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
12 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202116A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012
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 · = 441.1kΩ
0.5V + 11 · 3.7V - 1.1
1.1
choose R3 = 442kΩ.
The maximum output voltage with the selected values of
R4, R3 is
VOUT(MAX) = VOVP(MAX) · + 1
R
3
R4
1.3V · + 1
442kΩ
12.1kΩ
==
48.8V
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 =
=
5.23kΩ
262 · 0.6V
30mA
Maximum ILED Current (mA) R2 (kΩ)
30 5.23
25 6.19
20 7.87
15 10.5
10 15.8
5 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 condi-
tions. Forward voltage (VF) and package thermal resis-
tance (θJA) are the dominant factors to consider in select-
ing 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 con-
duction period. Manufacturers’ datasheets should be
consulted to verify reliability under peak loading condi-
tions. 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 approximate power loss on the Schottky diode can
be calculated:
I
AVG
= I
OUT
The average output current multiplied by the forward
diode voltage determines the loss of the output diode.
P
LOSS-DIODE
= I
AVG
· V
F
= I
OUT
· V
F
Diode junction temperature can be estimated.
T
J
= T
AMB
+ θ
JA
· P
LOSS-DIODE
AAT1405
DATA SHEET
Four-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
13
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202116A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012
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 mini-
mized 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 con-
sidered to maintain low quiescent (input) current and
high efficiency under light load. The rectifier reversed
current increases dramatically at elevated temperatures.
Inductor Selection
The white LED boost (step-up) converter is designed to
operate with an inductor with a minimum value of 4.7μH
for all input and output voltage combinations. The induc-
tor saturation current rating should be greater than the
NMOS current at maximum duty cycle.
DMAX =
(V
OUT
+ V
F
- V
IN(MIN)
)
VOUT + VF
The inductor (L) is selected to avoid saturation at mini-
mum input voltage, maximum output load conditions.
Peak current may be calculated from the following equa-
tion, again assuming continuous conduction mode.
Worst-case peak current occurs at minimum input volt-
age (maximum duty cycle) and maximum load.
IPEAK = +
I
OUT
1 - DMAX
D
MAX
· V
IN(MIN)
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 recom-
mended 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 =
I
OUT
· D
MAX
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 AAT1405 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) sys-
tem in frequency domain. The dominant pole can be
calculated by:
fP =
1
2π · R0 · C4
AAT1405
DATA SHEET
Four-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
14 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202116A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012
The ESR zero of the output capacitor (see Figure 3) can
be calculated by:
fZ_ESR =
1
2π · RESR · C4
Where:
C4 is the output filter capacitor
RO is the equivalent load resistor value
RESR is the equivalent series resistance of the output
capacitor.
The right half plane (RHP) zero can be calculated by:
fZ_ESR = VIN2
2π · L1 · IOUT · VOUT
C4
D1
L1
RO
ESR
VIN
VOUT
IOUT
Figure 3: AAT1405 Equivalent Output Stage.
It is recommended to design the bandwidth to one
decade lower than the frequency of RHP zero to guaran-
tee the loop stability. A series capacitor and resistor
network (R1 and C3) connected to the COMP pin sets the
pole and zero which are given by:
fP_COM =
1
2π · REA · C3
fZ_COM =
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.
AAT1405
DATA SHEET
Four-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
15
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202116A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012
R3
442k
R4
12.1k
MSS1P6
D1
V
IN
5V - 26V
C4
2.2µF
50V
0805
R2
7.5k
R1
4.99k
C1
10µF
35V
C2
2.2µF
10V C3
15nF
JP5
JP2
VOUT
PWM
5
CS2
9
GND
CS1
8
CS3
6
CS4
7
SGND
GND
GND
GND
GND
11
RSET
15
COMP
16
OVP 17
GND
GND
FSET
2
SYNC
1
12
13
14
LX
19
PGND
GND
IN
24 EN
23
VCC
22
AAT1405
U1
TQFN34-24
4 LEDs in series
4
3
10
18
21
20
EP
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 15nF, 10V, 0603
C4 Murata, GRM31CR71H225KA88L, 2.2μF, 50V, X7R, 1206
R1, R2, R3, R4 Carbon Film resistors, 1%, 0603
L1 4.7μH
JP1
JP3
Figure 4: AAT1405IMK Evaluation Board Schematic.
Figure 5: AAT1405IMK Evaluation Board Figure 6: AAT1405IMK Evaluation Board
Top Side Layout. Bottom Side Layout.
AAT1405
DATA SHEET
Four-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
16 Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
202116A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012
Copyright © 2012 Skyworks Solutions, Inc. All Rights Reserved.
Information in this document is provided in connection with Skyworks Solutions, Inc. (“Skyworks”) products or services. These materials, including the information contained herein, are provided by Skyworks as a
service to its customers and may be used for informational purposes only by the customer. Skyworks assumes no responsibility for errors or omissions in these materials or the information contained herein. Sky-
works may change its documentation, products, services, specications or product descriptions at any time, without notice. Skyworks makes no commitment to update the materials or information and shall have no
responsibility whatsoever for conicts, incompatibilities, or other difculties arising from any future changes.
No license, whether express, implied, by estoppel or otherwise, is granted to any intellectual property rights by this document. Skyworks assumes no liability for any materials, products or information provided here-
under, including the sale, distribution, reproduction or use of Skyworks products, information or materials, except as may be provided in Skyworks Terms and Conditions of Sale.
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
PURPOSE OR USE, MERCHANTABILITY, PERFORMANCE, QUALITY OR NON-INFRINGEMENT OF ANY INTELLECTUAL PROPERTY RIGHT; ALL SUCH WARRANTIES ARE HEREBY EXPRESSLY DISCLAIMED. SKYWORKS DOES
NOT WARRANT THE ACCURACY OR COMPLETENESS OF THE INFORMATION, TEXT, GRAPHICS OR OTHER ITEMS CONTAINED WITHIN THESE MATERIALS. SKYWORKS SHALL NOT BE LIABLE FOR ANY DAMAGES, IN-
CLUDING BUT NOT LIMITED TO ANY SPECIAL, INDIRECT, INCIDENTAL, STATUTORY, OR CONSEQUENTIAL DAMAGES, INCLUDING WITHOUT LIMITATION, LOST REVENUES OR LOST PROFITS THAT MAY RESULT FROM
THE USE OF THE MATERIALS OR INFORMATION, WHETHER OR NOT THE RECIPIENT OF MATERIALS HAS BEEN ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
Skyworks products are not intended for use in medical, lifesaving or life-sustaining applications, or other equipment in which the failure of the Skyworks products could lead to personal injury, death, physical or en-
vironmental damage. Skyworks customers using or selling Skyworks products for use in such applications do so at their own risk and agree to fully indemnify Skyworks for any damages resulting from such improper
use or sale.
Customers are responsible for their products and applications using Skyworks products, which may deviate from published specications as a result of design defects, errors, or operation of products outside of pub-
lished parameters or design specications. Customers should include design and operating safeguards to minimize these and other risks. Skyworks assumes no liability for applications assistance, customer product
design, or damage to any equipment resulting from the use of Skyworks products outside of stated published specications or parameters.
Skyworks, the Skyworks symbol, and “Breakthrough Simplicity” are trademarks or registered trademarks of Skyworks Solutions, Inc., in the United States and other countries. Third-party brands and names are for
identication purposes only, and are the property of their respective owners. Additional information, including relevant terms and conditions, posted at www.skyworksinc.com, are incorporated by reference.
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.
Ordering Information
Package Marking1Part Number (Tape and Reel)2
TQFN34-24 K3XYY AAT1405IMK-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
4.000 ± 0.050
Top View Bottom View
Side View
Detail “A”
1.700 ± 0.050
Detail “A”
R(5x)
Index Area
0.210 ± 0.040
2.700 ± 0.050
0 + 0.10
- 0.00
0.750 ± 0.050
0.203 REF
0.400 BSC
0.400 ± 0.050
All dimensions in millimeters.
