AAT1405 - Skyworks Solutions, Inc.

DATA SHEET
AAT1405
Four-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
General Description
Features
The AAT1405 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. Four precision current 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 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 AAT1405 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: 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
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.
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
DATA SHEET
AAT1405
Four-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
Typical Application
VIN: 4.5V – 26V
C1
2.2µF
50V
0805
L1 4.7µH
C2
2.2µF
6.3V
0603
D1
EN
VIN
VCC
R1
2
R2
VOUT: 45V at 120mA
R3
OVP
AAT1405
TQFN34-24
R4
PWM
SYNC
C3
LX
Up to 44 WLED Backlight
COMP
RSET
FSET
CS1
CS2
CS3
CS4
PGND GND SGND
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
C4
2.2µF
50V
0805
DATA SHEET
AAT1405
Four-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, 8, 9, 13,
14, 18, 21
GND
GND
5
PWM
I
6
7
10
11
12
15
16
CS1
CS2
SGND
CS3
CS4
RSET
COMP
O
O
GND
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 100Hz-100kHz
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.
Current sink ground tied to return of internal current sinks CS1-CS4.
Output current sink 3. Connect to SGND to disable channel 3.
Output current sink 4. Connect to SGND to disable channel 4.
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
16
5
15
6
14
7
13
8
9
10
11
LX
GND
OVP
COMP
RSET
GND
GND
12
CS4
CS3
SGND
GND
GND
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
3
DATA SHEET
AAT1405
Four-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 – CS4 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 VCC + 0.3
134
-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
80 to 120
-40 to 85
-40 to 125
V
kHz
mA
°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
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
DATA SHEET
AAT1405
Four-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
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
ICSx-Matching
VOVP
RDS(ON)LO
DMAX
TMIN
ICSx/IRSET
ILIMIT
ILEAK
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-CS4 = Open, EN = Logic Low,
does not include LX leakage current
ICSx = 21mA
4.5
5.0
-5
ICSx = 21mA
VOUT Rising
VOUT Falling
VCC = 4.5V
5.5
26.0
4.3
500
3.2
4.0
4.5
6
V
1.5
mA
40.0
µA
±2
+5
%
-3
±2
+3
%
1.1
1.2
100
200
1.3
6.5
1
10
V
mV
mΩ
%
ns
A/A
A
µA
µA
100
262
ICSx/IRSET, VRSET = 0.6V
3.0
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
EN =
EN =
FSET
VIN =
FSET
VIN =
V
1
V
V
µA
µs
140
15
°C
°C
1.4
-1
1
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 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
202116A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012
5
DATA SHEET
AAT1405
Four-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 = 120mA)
70
60
50
40
VOUT = 29V
VOUT = 36V
30
8
10
12
14
16
18
20
22
24
60
50
40
20
40
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 (%)
50
40
30
20
10
0
20
40
60
80
VCC Line Regulation vs. Input Voltage
5
4.7
4.65
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
10
35
Temperature (°C)
60
100
PWM Duty Cycle (%)
4.8
-15
180
60
0
VCC (V)
Current Limit (A)
160
70
(VIN = 5V to 26V)
6
140
80
Low Side Switch Current Limit vs. Temperature
3.4
-40
120
(VIN = 12V; ICSX = 20mA/ch)
90
0
100
Output Current vs. PWM Duty Cycle
100
20
80
(L = 10µH; VCC = 4.7V; FSET = GND)
30
60
Output Current (mA)
Boost Efficiency vs. PWM Duty Cycle
40
VIN = 9V, VOUT = 28V
VIN = 12V, VOUT = 36V
VIN = 24V, VOUT = 46V
30
20
6
70
6
85
11
16
21
Input Voltage (V)
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
26
DATA SHEET
AAT1405
Four-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
1.3
1.25
1.2
1.15
85°C
25°C
-40°C
1.1
1.05
1
6
9
12
15
18
21
Shutdown Current (µA)
Quiescent Current (mA)
1.4
1.35
18
16
14
12
10
8
6
85°C
25°C
-40°C
4
2
0
24
6
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
1.26
1.24
1.22
1.2
1.18
1.16
1.14
1.12
1.1
-40
85
-15
Temperature (°C)
Current Sink Matching (%)
Current Sink Accuracy (%)
3
2
1
0
-1
-2
-3
35
Temperature (°C)
60
85
(VIN = 12V; VCSX = 0.8V; ICSX = 21mA/Channel)
4
10
35
Current Sink Matching vs. Temperature
(VIN = 12V; VCSX = 0.8V; ICSX = 21mA/Channel)
-15
10
Temperature (°C)
Current Sink Accuracy vs. Temperature
-4
-40
26
(VIN = 12V)
4
-15
22
Over-Voltage Threshold vs Temperature
(VIN = 12V)
-4
-40
18
Input Voltage (V)
Switching Frequency vs. Temperature
-3
14
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
202116A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012
7
DATA SHEET
AAT1405
Four-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 = 80mA)
VIN
(AC coupled)
(50mV/div)
EN/SET
(10V/div)
VOUT
(20V/div)
IOUT
(50mA/div)
(VIN = 12V; VOUT = 37V; COUT = 2.2μF;
L = 4.7µH; IOUT = 80mA)
VOUT
(AC coupled)
(200mV/div)
12V
ILX
(1A/div)
ILX
(1A/div)
Time (100µs/div)
Time (500ns/div)
PWM Switching Waveforms
(VIN = 12V; VOUT = 37V; COUT = 2.2μF;
L = 4.7µH; IOUT = 80mA)
PWM
(5V/div)
VOUT
(1V/div)
37V
IOUT
(50mA/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
202116A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012
DATA SHEET
AAT1405
Four-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
Functional Block Diagram
IN
LX
Linear Reg
VCC
CS1
EN
OVP
COMP
FSET
P
Logic
PWM
SYNC
CS2
VREF
CS3
Osc
CS4
S
P
GND
S
PGND SGND
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 forward 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 possible 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
RSET
increased current capability. Thus, the AAT1405 allows
operation with fewer than 4 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 120mA per LED
string.
The AAT1405 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
adjustable up to 1300kHz for optimum efficiency and the
smallest external filtering components. Alternatively, the
device may be synchronized to an external clock.
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
9
DATA SHEET
AAT1405
Four-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
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 Operation
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.
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 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.
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
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
The AAT1405 device is protected from faults arising from
LED opens and/or shorts.
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
202116A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 29, 2012
DATA SHEET
AAT1405
Four-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
Application Information
The maximum voltage of each LED string including the
current sink headroom should not exceed VOUT(MIN).
OVP Protection with Open LED Failure
VOUT(MIN) > VCSX + N · VFLED(MAX)
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 ·
VOUT(MAX)
-1
VOVP(MAX)
VOVP(MIN) ·
R3
+ 1 > VCSX + N · VFLED(MAX)
R4
R3 > R4 ·
VCSX + N · VFLED(MAX) - VOVP(MIN)
VOVP(MIN)
Where:
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.
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 resistive divider is that the maximum voltage at the LX pin
should not exceed VLX(MAX) = 50V.
VLX(MAX) = VOUT(MAX) + VD1 + VRING
The output voltage at the minimum OVP threshold is
VOUT(MIN) = VOVP(MIN) ·
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.
R3
+1
R4
Measurements should confirm that the maximum switching node voltage VLX(MAX) is less than 50V under worst case
conditions.
L1
D1
VOUT
VIN
VCC
C4
C1
LX
R3
IR2
OVP
VRSET = 0.6V
264 .I R2
R4
1.2V
R2
Figure 2: Over-Voltage Protection and Current Sink Setting Circuit.
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11
DATA SHEET
AAT1405
Four-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
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
= 441.1kΩ
1.1
choose R3 = 442kΩ.
The maximum output voltage with the selected values of
R4, R3 is
R3
442kΩ
+ 1 = 1.3V ·
+ 1 = 48.8V
R4
12.1kΩ
VOUT(MAX) = VOVP(MAX) ·
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)
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 approximate power loss on the Schottky diode can
be calculated:
IAVG = IOUT
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.
The average output current multiplied by the forward
diode voltage determines the loss of the output diode.
PLOSS-DIODE = IAVG · VF = IOUT · VF
262 · 0.6V
R2 =
= 5.23kΩ
30mA
Diode junction temperature can be estimated.
TJ = TAMB + θJA · PLOSS-DIODE
Maximum ILED Current (mA)
R2 (kΩ)
30
25
20
15
10
5
5.23
6.19
7.87
10.5
15.8
31.6
Table 2: Maximum LED Current Sink
vs. RSET Resistor (R2) Values.
12
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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DATA SHEET
AAT1405
Four-Channel LED Backlight Driver
with Integrated Boost and High Frequency Direct PWM Dimming
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 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 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 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) system in frequency domain. The dominant pole can be
calculated by:
fP =
1
2π · R0 · C4
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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13
DATA SHEET
AAT1405
Four-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 =
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:
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.
fP_COM =
The right half plane (RHP) zero can be calculated by:
fZ_ESR =
VIN
fZ_COM =
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
VOUT(2.97MΩ).
L1
D1
A 15nF (C3) capacitor and a 5kΩ (R1) resistor in series
are chosen for optimum phase margin and fast transient
response.
ESR
RO
I OUT
C4
Figure 3: AAT1405 Equivalent Output Stage.
14
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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DATA SHEET
AAT1405
Four-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
JP5
16
R1
4.99k
JP3
R2
7.5k
2
1
OVP
17
C4
2.2µF
50V
0805
R4
12.1k
VCC
PWM
AAT1405
RSET
FSET
SYNC
6
CS1
7
CS2
11
CS3
12
CS4
8
GND
9
GND
13
GND
14
GND
EP
20
PGND
21
GND
18
GND
4
GND
3
GND
10
SGND
JP2
15
LX
EN
IN
COMP
4 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 15nF, 10V, 0603
C4 Murata, GRM31CR71H225KA88L, 2.2μF, 50V, X7R, 1206
R1, R2, R3, R4 Carbon Film resistors, 1%, 0603
Figure 4: AAT1405IMK Evaluation Board Schematic.
Figure 5: AAT1405IMK Evaluation Board Top Side Layout.
Figure 6: AAT1405IMK Evaluation Board
Bottom Side Layout.
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
15
DATA SHEET
AAT1405
Four-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
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
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.
Copyright © 2012 Skyworks Solutions, Inc. All Rights Reserved.
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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. Skyworks may change its documentation, products, services, specifications 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 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
PURPOSE OR USE, MERCHANTABILITY, PERFORMANCE, QUALITY OR NON-INFRINGEMENT OF ANY INTELLECTUAL PROPERTY RIGHT; ALL SUCH WARRANTIES ARE HEREBY EXPRESSLY DISCLAIMED. SKYWORKS DOES
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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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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