AAT2847 - Skyworks Solutions, Inc.

DATA SHEET
AAT2847
Four-Channel Backlight Driver with Dual LDOs
General Description
Features
The AAT2847 is a highly integrated power solution for
single cell Li-Ion/Polymer based liquid crystal display
(LCD) display applications. It includes a four channel
light emitting diode (LED) backlight driver and two integrated 200mA low dropout voltage regulators (LDOs) as
additional power supplies for display and camera related
chipsets.
• Input Supply Voltage Range: 2.7V to 5.5V
• Tri-Mode (1X/1.5X/2X) Charge Pump:
▪ Delivers up to 120mA of Output Current
• Integrated LCD Display Solution:
▪ Four-Channel WLED Backlight
• User-Programmable WLED Current Scales: 30mA,
20mA and 15mA.
▪ Sixteen Programmable Current Level Settings
• User Selectable Low Level Current Scale
▪ Four Programmable Current Level Settings
Dual
200mA LDOs (w/Separate Enables)
▪
• Single-Wire AS2Cwire Serial Interface for Configuration/
Control
▪ Four Addressable Registers
▪ Fast, 1MHz Serial Interface
• > 90% Peak Efficiency
• LDO Output Voltages:
▪ AAT2847-EE: User-Programmable
▪ AAT2847-QG: 2.8V and 1.5V
▪ AAT2847-QI: 2.8V and 1.8V
• Over-Temperature Protection
• Available in 3x4x0.75mm TQFN34-20 Package
• -40°C to +85°C Temperature Range
The backlight driver in the AAT2847 is a low noise trimode DC/DC charge pump converter. Each of the four
channels of the backlight driver is capable of delivering
up to 20mA of bias currents for white LEDs. The white
LED (WLED) backlight bias current matching is 1% which
helps provide uniform display brightness.
Skyworks' AS2Cwire™ (Advanced Simple Serial Control™)
serial digital interface is used to enable, disable, and set
the current for each backlight LED channel. Each LED
channel has sixteen available current level settings in
three separate current scales, plus four available current
level settings on a low level current scale.
Each LED channel is equipped with built-in short circuit
protection and auto disable functionality. A low shutdown
current feature disconnects the load from the input and
reduces quiescent current to less than 1μA.
The AAT2847 is available in the thermally enhanced
20-pin 3x4x0.75mm TQFN package.
Applications
•
•
•
•
Camera Function Power Supplies
Camera Phone Displays
LCD Modules
White LED Backlighting
Typical Application
C1
1μF
C2
1μF
C1- C1+ C2-
C1
1μF
C2
1μF
C2+
C1- C1+ C2-
OUT
WLEDs
OSRAM LW M673
or equivalent
C OUT
1μF
IN
VBAT
3.6V
D2
D3
D1
D2
D3
D4
CIN
2.2μF
D4
IN
LDOA
200mA
IN
C LDOA
2.2μF
AS2Cwire
Backlight Control
LDO A Enable
LDO B Enable
FBA
EN/SET
ENA
LDOB
FBB
GND
200mA
C LDOB
2.2μF
ENB
WLEDs
OSRAM LW M673
or equivalent
AAT 2847-QI
D1
C IN
2.2μF
COUT
1μF
IN
AAT 2847-EE
VBAT
3.6V
C2+
OUT
AS2Cwire
Backlight control
CLDOA
2.2μF
EN/SET
LDO A Enable
ENA
LDO B Enable
ENB
VOUTA
2.8V, 200mA
LDOA
VOUTB
1.8V, 200mA
LDOB
CLDOB
2.2μF
GND
PGND
PGND
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202068A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012
1
DATA SHEET
AAT2847
Four-Channel Backlight Driver with Dual LDOs
Pin Descriptions
Symbol
Pin #
AAT2847-EE
AAT2847-QG/QI
1
D2
D2
2
D1
D1
3
4, 6
5
LDOB
IN
PGND
LDOB
IN
PGND
7
FBA
NC
8
9
10
LDOA
C2C2+
LDOA
C2C2+
11
OUT
OUT
12
13
14
15
C1C1+
EN/SET
ENB
C1C1+
EN/SET
ENB
16
D4
D4
17
D3
D3
18
19
GND
ENA
GND
ENA
20
FBB
N/C
EP
Function
LED2 current channel input. Connect to the cathode of backlight LED 2. If not
used, connect D2 to the OUT pin.
LED1 current channel input. Connect to the cathode of backlight LED 1. If not
used, connect D1 to the OUT pin.
Output of LDOB.
Input voltage supply connection.
Power Ground.
AAT2847-EE: Feedback pin of LDOA. Internally regulated at 1.2V.
AAT2847-QG/QI: No connection. Do not make any connection to this pin.
Output of LDOA.
Negative terminal of flying capacitor 2.
Positive terminal of flying capacitor 2.
Charge pump output to drive load circuit. Connect a 1μF or larger ceramic capacitor between OUT and PGND.
Negative terminal of flying capacitor 1.
Positive terminal of flying capacitor 1.
AS2Cwire control pin for backlight LED current profile selection and control.
Enable pin for LDOB. Active logic high.
LED4 current channel input. Connect to the cathode of backlight LED 4. If not
used, connect D4 to the OUT pin.
LED3 current channel input. Connect to the cathode of backlight LED 3. If not
used, connect D3 to the OUT pin.
Ground.
Enable pin for LDOA. Active logic high.
AAT2847-EE: Feedback pin of LDOB. Internally regulated at 1.2V.
AAT2847-QG/QI: No connection. Do not make any connection to this pin.
Exposed pad (bottom).
Pin Configuration
AAT2847-EE
TQFN34-20
(Top View)
AAT2847-QG/QI
TQFN34-20
(Top View)
15
3
14
4
13
5
12
6
11
D4
ENB
EN/SET
C1+
C1OUT
D2
D1
LDOB
IN
PGND
IN
17
16
2
18
1
19
20
17
18
19
20
1
16
2
15
3
14
4
13
5
12
6
11
D4
ENB
EN/SET
C1+
C1OUT
9
10
8
7
9
10
8
7
C2+
C2LDOA
N/C
C2+
C2LDOA
FBA
2
D3
GND
ENA
N/C
D3
GND
ENA
FBB
D2
D1
LDOB
IN
PGND
IN
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202068A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012
DATA SHEET
AAT2847
Four-Channel Backlight Driver with Dual LDOs
Absolute Maximum Ratings1
TA = 25°C, unless otherwise noted. Pin descriptions below apply to AAT2847-EE (AAT2847-QG/QI)
Symbol
VN
VN
VN
TJ
TLEAD
Description
[IN, OUT, D1, D2, D3, D4] to GND
[C1+, C1-, C2+, C2-] to GND
[LDOA, LDOB, FBA, FBB, EN/SET, ENA, ENB] to GND
Operating Temperature Range
Maximum Soldering Temperature (at leads, 10 sec)
Value
Units
-0.3 to 6.0
-0.3 to VOUT + 0.3
-0.3 to VIN + 0.3
-40 to 150
300
V
V
V
°C
°C
Value
Units
50
2
°C/W
W
Thermal Information2, 3
Symbol
θJA
PD
Description
Thermal Resistance
Maximum Power Dissipation
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 in not implied. Only one Absolute Maximum Rating should be applied at any one time.
2. Derate 20mW/°C above 40°C ambient temperature.
3. Mounted on a FR4 circuit board.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202068A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012
3
DATA SHEET
AAT2847
Four-Channel Backlight Driver with Dual LDOs
Electrical Characteristics1
VIN = 3.6V; CIN = CLDOA = CLDOB = 2.2μF; COUT = 1μF; C1 = C2 = 1μF; TA = 25°C, unless otherwise noted. Typical values
are at TA = 25°C.
Symbol
Description
Power Supply
Input Voltage Range
VIN
ISHDN
Total Shutdown Current at IN
Charge Pump
IIN
IDX
I(D-Match)
Input Operating Current
Average Current Accuracy
Current Matching2
1x to 1.5x or 1.5x to 2x Transition
VTH
Threshold at Any DX Pin
fCLK
Clock Frequency
TSD
Over-Temperature Shutdown Threshold
THYS
Over-Temperature Shutdown Hysteresis
EN/SET Logic Control
TEN/SET LO
EN/SET Low Time
TEN/SET_HI_MIN Minimum EN/SET High Time
TEN/SET_HI_MAX Maximum EN/SET High Time
TOFF
EN/SET Off Timeout
TLAT
EN/SET Latch Timeout
VIL(EN/SET)
EN/SET Logic Low Threshold Voltage
VIH(EN/SET)
EN/SET Logic High Threshold Voltage
IEN/SET
EN/SET Input Leakage
Conditions
Min
Typ
Max
Units
5.5
1.0
V
μA
2.7
VEN/SET = VENA = VENB = 0V
1x Mode, 3.0  VIN 5.5, Active, No Load,
VENA = VENB = 0V
1.5x Mode, 3.0  VIN 5.5, Active, No Load,
VENA = VENB = 0V
2x Mode, 3.0  VIN 5.5, Active, No Load,
VENA = VENB = 0V
DATA 1, 20mA Range
DATA 2, ADDRESS 4
DATA 1, 30mA Range
DATA 1, 15mA Range
VIN - VF = 1.5V, 20mA Range
1.0
4.0
5.0
18
0.9
20mA Range
20
1.0
30
15
0.5
22
1.1
1
mA
%
150
mV
1
140
15
MHz
°C
°C
0.3
75
50
75
500
500
0.4
VEN/SET = VIN = 5V
mA
1.4
-1
1
μs
ns
μs
μs
μs
V
V
μA
1. The AAT2847 is guaranteed to meet performance specifications over the –40°C to +85°C operating temperature range is assured by design, characterization and correlation
with statistical process controls.
2. Current matching is defined as the deviation of any sink current from the average of all active channels.
4
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202068A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012
DATA SHEET
AAT2847
Four-Channel Backlight Driver with Dual LDOs
Electrical Characteristics1
VIN = 3.6V; CIN = CLDOA = CLDOB = 2.2μF; COUT = 1μF; C1 = C2 = 1μF; TA = 25°C, unless otherwise noted. Typical values
are at TA = 25°C.
Symbol
Description
Conditions
Min
Typ
Max
80
60
1.2
150
150
112
1.23
300
Units
LDOs: AAT2847-EE
IIN
IN Operating Current
Feedback Voltage
VFBA, VFBB
VDO
Dropout Voltage
VOUT/
Line Regulation
VOUT*VIN
PSRR
Power Supply Rejection Ratio
LDOs: AAT2847-QG
IIN
LDOA
LDOB
VDO
VLDO[A/B]/
VLDO[A/B]*VIN
LDOA
LDOB
VDO
VLDO[A/B]/
VLDO[A/B]*VIN
LDOA, LDOB Line Regulation
VIN = (LDOA + 1V) to 5V; VIN = (LDOB + 1.2V) to 5V
2.716
1.455
ILDO[A/B] =10mA, 1kHz
LDOA Voltage Tolerance
LDOB Voltage Tolerance
LDOA Dropout Voltage2
VENA = VENB = VIN, VEN/SET = 0V, No Load
VENA = VIN; VENB = 0V; VEN/SET = 0V; No Load
ILDOA = 1mA to 150mA
ILDOB = 1mA to 150mA
ILDOA = 150mA
LDOA, LDOB Line Regulation
VIN = (LDO[A/B] + 1V) to 5V
IN Operating Current
LDOA, LDOB Power Supply
Rejection Ratio
LDO Logic Control – All Options
VIL(ENA),
ENA, ENB Input Logic Low
VIL(ENB)
Threshold Voltage
VIH(ENA),
ENA, ENB Input Logic High
VIH(ENB)
Threshold Voltage
IEN[A/B]
ENA, ENB Input Leakage
PSRR
ILDO[A/B] =10mA, 1kHz
LDOA Voltage Tolerance
LDOB Voltage Tolerance
LDOA Dropout Voltage2
LDOA, LDOB Power Supply
Rejection Ratio
LDOs: AAT2847-QI
1.17
VIN = (VLDO[A/B] + 1V) to 5V
VENA = VENB = VIN, VEN/SET = 0V, No Load
VENA = VIN; VENB = 0V; VEN/SET = 0V; No Load
ILDOA = 1mA to 150mA
ILDOB = 1mA to 150mA
ILDOA = 150mA
IN Operating Current
PSRR
IIN
VENA = VENB = VIN, VEN/SET = 0V, No Load
VENA = VIN; VENB = 0V; VEN/SET = 0V; No Load
ILDO[A/B] = 1mA to 200mA
ILDO[A/B] = 150mA
2.716
1.746
ILDO[A/B] = 10mA, 1kHz
V
mV
0.09
%/V
50
dB
80
60
2.8
1.5
150
150
112
2.884
1.545
300
μA
V
V
mV
0.09
%/V
50
dB
80
60
2.8
1.8
150
150
112
2.884
1.854
300
μA
V
V
mV
0.09
%/V
50
dB
0.4
1.4
VEN[A/B] = VIN = 5V
μA
-1
V
V
1
μA
1. The AAT2847 is guaranteed to meet performance specifications over the –40˚C to +85°C operating temperature range is assured by design, characterization and correlation
with statistical process controls.
2. VDO is defined as VIN - LDOA when LDOA is 98% of nominal.
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202068A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012
5
DATA SHEET
AAT2847
Four-Channel Backlight Driver with Dual LDOs
Typical Characteristics
Backlight Efficiency vs. Input Voltage
Backlight Current Matching vs. Temperature
(IOUT = 20mA/Channel; VIN = 4.2V)
100
21
80
LED Current (mA)
Efficiency (%)
90
20mA/Channel
70
60
1mA/Channel
50
40
30
2.7
3.1
3.5
14.5mA/Channel
3.9
4.3
4.7
5.1
10
35
60
85
EN/SET Off Timeout vs. Input Voltage
400
-40°C
350
-40°C
300
TOFF (µs)
250
200
150
25°C
85°C
2.7
3.1
3.5
3.9
200
4.3
4.7
5.1
50
2.7
5.5
25°C
85°C
100
3.1
3.5
3.9
4.3
4.7
5.1
Input Voltage (V)
Input Voltage (V)
Logic High Threshold Voltage
vs. Input Voltage
Logic Low Threshold Voltage
vs. Input Voltage
1.0
0.9
0.8
0.7
0.6
25°C
0.5
85°C
0.4
0.3
3.1
3.5
5.5
1.2
-40°C
1.1
2.7
250
150
VIL(ENA/ENB), VIL(EN/SET) (V)
TLAT (µs)
-15
EN/SET Latch Timeout vs. Input Voltage
1.2
VIH(ENA/ENB), VIH(EN/SET) (V)
19
Temperature (°C)
100
3.9
4.3
Input Voltage (V)
6
19.5
Input Voltage (V)
300
0.2
20
18.5
-40
5.5
350
50
20.5
4.7
5.1
5.5
1.1
-40°C
1.0
0.9
0.8
0.7
0.6
0.5
25°C
0.4
85°C
0.3
0.2
2.7
3.1
3.5
3.9
4.3
4.7
Input Voltage (V)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202068A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012
5.1
5.5
DATA SHEET
AAT2847
Four-Channel Backlight Driver with Dual LDOs
Typical Characteristics
Shutdown Current vs. Input Voltage
Backlight Operating Characteristic
(VEN/SET = VENA/ENB = 0V)
(VIN = 3.7V; 1.5X Mode; 20mA/Channel Load;
AC Coupled)
Shutdown Current (nA)
20
VIN
(20mV/div)
-40°C
15
VOUT
(40mV/div)
10
0
85°C
25°C
5
VDX
(20mV/div)
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Time (500ns/div)
Input Voltage (V)
Backlight Operating Characteristic
Backlight Operating Characteristic
(VIN = 3.5V; 1.5X Mode; 14mA/Channel Load;
AC Coupled)
(VIN = 2.9V; 2X Mode; 20mA/Channel Load;
AC Coupled)
VIN
(20mV/div)
VIN
(20mV/div)
VOUT
(40mV/div)
VOUT
(40mV/div)
VDX
(20mV/div)
VDX
(40mV/div)
Time (500ns/div)
Time (500ns/div)
Backlight Operating Characteristic
(VIN = 2.9V; 2X Mode; 14mA/Channel Load;
AC Coupled)
VIN
(20mV/div)
VOUT
(40mV/div)
VDX
(40mV/div)
Time (500ns/div)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202068A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012
7
DATA SHEET
AAT2847
Four-Channel Backlight Driver with Dual LDOs
Typical Characteristics
Turn On to 1X Mode Backlight
Turn On to 1.5X Mode Backlight
(20mA/Channel; Address 0, Data 1; VIN = 4.2V)
(20mA/Channel; Address 0, Data 1; VIN = 3.5V)
VEN/SET
(2V/div)
VEN/SET
(2V/div)
VOUT
(2V/div)
VOUT
(2V/div)
VDX
(500mV/div)
VDX
(500mV/div)
IIN
(100mA/div)
IIN
(200mA/div)
Time (200µs/div)
Time (500ns/div)
Turn On to 2X Mode Backlight
Turn Off from 1.5X Mode Backlight
(20mA/Channel; Address 0, Data 1; VIN = 3.2V)
(20mA/Channel; Address 0, Data 1; VIN = 3.6V)
VEN/SET
(2V/div)
VEN/SET
(2V/div)
VOUT
(2V/div)
VOUT
(2V/div)
VDX
(500mV/div)
ILED
(20mA/div)
IIN
(200mA/div)
Time (200µs/div)
Time (100µs/div)
1.0
LDOA
0.5
0.0
-0.5
LDOB
-1.0
0.1
1
10
Load Current (mA)
8
LDOA/LDOB Line Regulation
Output Voltage Error (%)
Output Voltage Error (%)
LDOA/LDOB Load Regulation
100
1000
1.000
0.500
LDOA
0.000
LDOB
-0.500
-1.000
2.7
3.1
3.5
3.9
4.3
4.7
Input Voltage (V)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202068A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012
5.1
5.5
DATA SHEET
AAT2847
Four-Channel Backlight Driver with Dual LDOs
Typical Characteristics
LDOA/LDOB Quiescent Current vs. Input Voltage
LDOA Load Transient Response
(VOUT = 1.2V)
(VIN = 3.6V; VLDOA = 1.2V)
Quiescent Current (µA)
120
85°C
100
200mA
25°C
ILDOA
(100mA/div)
80
10mA
60
40
0
2.7
VLDOA
(100mV/div)
-40°C
20
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
Time (20µs/div)
LDOB Load Transient Response
LDOA Line Transient Response
(VIN = 3.6V; VLDOB = 1.2V)
(10mA Load)
200mA
ILDOB
(100mA/div)
VIN = 4.2V
10mA
VIN
(400mV/div)
VIN = 3.6V
VLDOB
(100mV/div)
VLDOA
(20mV/div)
Time (20µs/div)
Time (40µs/div)
LDOB Line Transient Response
(10mA Load)
VIN = 4.2V
VIN
(400mV/div)
VIN = 3.6V
VLDOB
(20mV/div)
Time (40µs/div)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202068A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012
9
DATA SHEET
AAT2847
Four-Channel Backlight Driver with Dual LDOs
Typical Characteristics
LDOA/LDOB Turn On
LDOA/LDOB Turn On
(VIN = 3.6V; VLDO(A/B) = 2.8V; DC Coupled)
(VIN = 3.6V; VLDO(A/B) = 1.8V; DC Coupled)
VEN(A/B)
(2V/div)
VEN(A/B)
(2V/div)
VLDO(A/B)
(1V/div)
VLDO(A/B)
(1V/div)
Time (40µs/div)
Time (40µs/div)
LDOA/LDOB Turn On
LDOA/LDOB Turn On
(VIN = 3.6V; VLDO(A/B) = 1.5V; DC Coupled)
(VIN = 3.6V; VLDO(A/B) = 1.2V; DC Coupled)
VEN(A/B)
(2V/div)
VEN(A/B)
(2V/div)
VLDO(A/B)
(500mV/div)
VLDO(A/B)
(500mV/div)
Time (40µs/div)
10
Time (40µs/div)
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
202068A • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice. • June 15, 2012
DATA SHEET
AAT2847
Four-Channel Backlight Driver with Dual LDOs
Functional Block Diagram
C1+
AAT 2847-EE
(AAT 2847-QG/-QI)
C1- C2+
C2-
Tri-Mode
(1x, 1.5x and 2x)
Charge Pump
IN
OUT
1.2V
Reference
1MHz
Oscillator
Voltage
Reference
6 x16 bit
ROM
2
EN/SET
AS Cwire
Interface
D/A
D1
D/A
D2
D/A
D3
D/A
D4
IN
LDOA (2.8V/2.8V)
LDO A
ENA
FBA (NC)
LDOB (1.5V/1.8V)
LDO B
ENB
FBB (NC)
(AAT 2847-QG/-QI)
GND
PGND
Functional Description
The AAT2847 is an integrated solution for LCD display
applications with a built-in four channel white LED driver
(charge pump) and dual 200mA LDO voltage regulators.
The AAT2847 incorporates a tri-mode charge pump with
load switch (1X) functionality and high efficiency (1.5X
or 2X) performance. To maximize power conversion efficiency, an internal sensing circuit monitors the voltage
required at each white LED cathode input pin (D1-D4)
and sets the load switch and charge pump mode based
on the input battery voltage and the white LED cathode
pin voltage. The voltage threshold for 1X to 1.5X and
1.5X to 2X mode transitions is VTH.
The charge pump in the AAT2847 starts-up in 1X mode
(default); under this condition, if the LED cathode input
pin voltage is below VTH the AAT2847 will transition into
1.5X mode. When 1.5X mode does not provide enough
current through the white LEDs for backlight applications, which occurs during the normal discharge of the
input battery power source, the LED cathode input pin
voltage will drop below VTH and the AAT2847 will transition into 2X mode. The charge pump requires only four
external capacitors, 1μF ceramic capacitors for the flying
(C1 and C2), input (CIN), and output (COUT) capacitors.
The four LED cathode input pins (D1-D4) can drive individual LEDs with a maximum current of 30mA each. The
unused LED cathode input pins have to be connected to
the OUT pin, otherwise the AAT2847 will operate in 2X
mode only. Operating in 2X mode when it is not necessary will result in a significant reduction in efficiency. The
AS2Cwire serial interface enables the charge pump and
sets the current flowing into the LED cathode input pins.
The AAT2847 also contains dual LDO voltage regulators
that have separate enable pins from each other and the
charge pump. The separate enable pins for each DC/DC
device in the AAT2847 allow for every possible device
operational combination. The two LDO regulators require
2.2μF output capacitors for stable operation.
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11
DATA SHEET
AAT2847
Four-Channel Backlight Driver with Dual LDOs
AS2Cwire Serial Interface Addressing
30.0
LED Current (mA)
25.0
20.0
15.0
10.0
Address 0
Address 4
5.0
Address
EN/SET Edges
Addressed Register
0
3
4
5
17
20
21
22
D1-D4 Current Control
Current Scale
Low Current Control
Independent LED Control
Table 1: AS2Cwire Serial Interface Addressing.
0.0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 1
2
3
4
Code
Figure 1: LED Current Control Profile.
AS2Cwire Serial Interface
Each white LED channel input on the AAT2847 (D1-D4) is
controlled by Skyworks' AS2Cwire serial digital interface.
The AS2Cwire interface uses the number of rising edges
on the EN/SET pin to address and load the LED configuration registers. AS2Cwire latches data or addresses after
the EN/SET pin has been held logic high for longer than
TLAT (500μs). Addresses and data are differentiated by
the number of EN/SET rising edges. Since the data registers are 4 bits each, the differentiating number of
pulses is 24 or 16, so that Address 0 is signified by 17
rising edges, Address 1 by 18 rising edges, Address 2 by
19 rising edges, and so on. Data is set to any number of
rising edges between, and including, 1 to 16.
A typical write protocol consist of the following: First a
burst of EN/SET rising edges that identify/target a particular address followed by EN/SET being held logic high
for the TLAT timeout period to latch the address value in
the address register, then another burst of rising edges
that signify data with the accompanying TLAT timeout
period to latch the data value in the data register. Once
an address is set, then multiple writes to the corresponding data register are allowed without having to write to
the address for every value change in the data register.
When EN/SET is held low longer than TOFF (500μs), the
AAT2847 enters shutdown mode operation and draws less
than 1μA from the input supply voltage. Data and address
registers are cleared (0 for the address register and 1 for
the data registers) in shutdown mode operation.
Current Operation (Address 0)
Use Address 0 to program all four LED channels with the
current values in Table 2. All four white LED channels are
programmed to the same current level by writing to
Address 0 followed by any Data between, and including,
1 to 16.
Current Scale (Address 3)
The AAT2847 has three selectable current scales for the
four white LED channels: 30mA, 20mA, and 15mA. Only
one of the three current scales can be active at any given
time. By default, the 20mA current scale is active upon
start-up. To change to the 30mA or 15mA current scale,
or go back to the 20mA scale, write to Address 3 with
the appropriate Data between, and including, 1 to 3. To
enable low current mode, write Data 4 to Address 3. Low
current mode results in the four white LED channels
reverting to the current set by the low current settings
in Address 4.
Data
30mA
Scale
20mA
Scale
15mA
Scale
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
30.0
28.5
26.6
25.2
23.3
21.8
19.8
18.5
16.5
15.0
13.1
11.6
9.8
8.3
6.3
4.8
20.0
19.0
17.7
16.8
15.5
14.5
13.2
12.3
11.0
10.0
8.7
7.7
6.5
5.5
4.2
3.2
15.0
14.3
13.3
12.6
11.6
10.9
9.9
9.2
8.3
7.5
6.5
5.8
4.9
4.1
3.2
2.4
Table 2: Current Settings—Address 0.
12
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DATA SHEET
AAT2847
Four-Channel Backlight Driver with Dual LDOs
Address
Data
T HI
T LO
TLAT
TLAT
EN/SET
1
2
Address
19
20
1
2...
n ≤ 16
0
3
DATA3
1
DATA0
1
n
Figure 2: AS2Cwire Serial Interface Timing.
Data
Current Scale
1
2
3
4
20mA Scale
30mA Scale
15mA Scale
Low Current Mode
Table 3: Current Scale Settings—Address 3.
Low Current Operation (Address 4)
All four LED channels are programmed to the same low
current level by writing to Address 4 followed by any
Data between, and including, 1 to 4. This operational
mode is especially useful for low current applications
where a continuous low current state is maintained for a
substantial length of time.
Data
mA
1
2
3
4
0.5
1.0
1.5
2.0
Table 4: Low Current Settings—Address 4.
Independent LED Current Control
(Address 5)
Independent LED control allows for individual LEDs to be
enabled and disabled to form custom arrangement of
active LEDs. To enable independent control write Address
5 with Data between, and including, 1 to 16.
Data
D4
D3
D2
D1
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
on
on
on
on
on
on
on
on
off
off
off
off
off
off
off
off
on
on
on
on
off
off
off
off
on
on
on
on
off
off
off
off
on
on
off
off
on
on
off
off
on
on
off
off
on
on
off
off
on
off
on
off
on
off
on
off
on
off
on
off
on
off
on
off
Table 5: Independent LED Control Settings—
Address 5.
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13
DATA SHEET
AAT2847
Four-Channel Backlight Driver with Dual LDOs
Auto Disable Feature
The charge pump in the AAT2847 is equipped with an
auto-disable feature for each LED channel. After the IC
is enabled and successively starts-up, a test current of
100μA (typical) is forced through each LED channel. The
channel will be disabled if the voltage on that particular
DX pin does not drop to certain threshold. This feature is
convenient for disabling an unused channel or during an
LED short circuiting event.
Low Dropout Regulators
The AAT2847 incorporates two LDO voltage regulators.
The two regulators run from the same 2.7V to 5.5V input
voltage as the charge pump and have separate ON/OFF
control inputs, ENA and ENB. For the AAT2847-EE, the
LDO output voltages are set through a resistive voltage
divider from the output (LDOA or LDOB) to the feedback
input (FBA or FBB). The ratio of the voltage divider resistor values determines the LDO output voltage. For the
AAT2847-QG option, LDOA is internally set to 2.8V and
LDOB is internally set to 1.5V. For the AAT2847-QI
option, LDOA is also 2.8V and LDOB is internally set to
1.8V. Each LDO regulator can supply a continuous load
current up to 200mA, and both LDOs include current
limiting and thermal overload protection to prevent damage to the load or to the LDO.
Thermal Protection
The charge pump has built-in thermal protection circuitry that will shut down the charge pump and the LDOs
if the die temperature rises above the thermal limit, as
is the case during an OUT pin short circuit event.
Applications Information
LED Selection
The charge pump in the AAT2847 is specifically intended
for driving white LEDs. However, the AAT2847 can drive
most types of LEDs with forward voltage specifications
ranging from 2.0V to 4.7V. LED applications may include
mixed arrangements for display backlighting, color (RGB)
LEDs, infrared (IR) diodes and any other load needing a
constant current source generated from a varying input
voltage. Since the D1 to D4 constant current channels
are matched with negligible voltage dependence, the
constant current channels will be matched regardless of
the specific LED forward voltage (VF) levels. Multiple
channels can be combined to obtain a higher LED drive
current without complication.
AAT2847-EE LDO Output
Voltage Programming
The output voltages for LDOA and LDOB are programmed
by an external resistor divider network. As shown in
Figure 3, the selection of R1 and R2 is a straightforward
matter. R1 is chosen by considering the tradeoff between
the feedback network bias current and resistor value.
Higher resistor values allow stray capacitance to become
a larger factor in circuit performance, whereas lower
resistor values decrease efficiency.
VLDO(A/B)
LDO(A/B)
R2(A/B)
FB(A/B)
VREF = 1.2V
R1(A/B)
Figure 3: Selection of External Resistors.
To select appropriate resistor values, first choose a value
for R1 that will produce a reasonable feedback network
bias current. Then, according to the desired VLDO(A/B), calculate R2 according to the equation below. An example
calculation follows.
R1 is chosen to be 120kΩ, resulting in a small feedback
network bias current of 10μA (VFB(A/B)/R1 = 1.2V/120kΩ).
The desired output voltage is 1.8V. From this information, R2 is calculated from the equation below:
14
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DATA SHEET
AAT2847
Four-Channel Backlight Driver with Dual LDOs
R2(A/B) =
R1(A/B)(VLDO(A/B) - 1.2V)
1.2V
The result is R2 = 60kΩ. Since 60kΩ is not a standard
1% resistor value, 60.4kΩ is selected. From this example calculation, for VOUT = 1.8V, use R1 = 120kΩ and R2
= 60.4kΩ. A table of example output voltages and corresponding resistor values is provided below.
R2 Standard 1% Values (R1 = 120kΩ)
VLDO(A/B) (V)
R2 (Ω)
2.8
2.5
2
1.8
1.5
160k
130k
79.6k
60.4k
30.1k
Table 6: Example Output Voltages and
Corresponding Resistor Values.
With an ideal 1.5X charge pump, the input current is
1.5X of the output current. The expression to define the
estimated ideal efficiency (η) for the AAT2847 in 1.5X
mode is as follows:
η=
PLEDs VLED1 · ILED1 + ... + VLED4 · ILED4
=
PIN
VIN · IIN
η=
4 · VLEDX · ILEDX
; x = 1, 2, 3 or 4 and IIN = 1.5(4 · ILEDX)
VIN · IIN
VLEDX
η = 1.5V
IN
The same calculations apply for the AAT2847 in 2X mode
where for an ideal 2X charge pump, the input current is
2X of the output current. The expression for the estimated ideal efficiency (η) for the AAT2847 in 2X mode is
as follows:
η=
PLEDs VLED1 · ILED1 + ... + VLED4 · ILED4
=
PIN
VIN · IIN
η=
4 · VLEDX · ILEDX
; x = 1, 2, 3 or 4 and IIN = 2(4 · ILEDX)
VIN · IIN
Device Power Efficiency
The AAT2847’s charge pump conversion efficiency is
defined as the power delivered to the white LED load
divided by the input power:
η=
PLEDs VLED1 · ILED1 + ... + VLED4 · ILED4
=
PIN
VIN · IIN
VLEDx = White LED Forward Voltage (VF)
ILEDx = White LED Bias Current (ID)
The expression to define the estimated ideal efficiency
(η) for the AAT2847 in 1X mode is as follows:
η=
PLEDs VLED1 · ILED1 + ... + VLED4 · ILED4
=
PIN
VIN · IIN
η=
4 · VLEDX · ILEDX
; x = 1, 2, 3 or 4 and IIN = 4 · ILEDX
VIN · IIN
VLEDX
η= V
IN
The AAT2847’s charge pump is a fractional charge pump
which will boost the input supply voltage in the event
where VIN is less then the required output voltage across
the white LED load. The efficiency can be simply defined
as a linear voltage regulator with an effective white LED
forward voltage that is equal to one and a half (1.5X
mode) or two (2X mode) times the input voltage.
VLEDX
η = 2V
IN
Capacitor Selection
Careful selection of the six external capacitors CIN, C1,
C2, CLDOA, CLDOB, and COUT are important because they will
affect turn on time, output ripple and transient performance. Optimum performance will be obtained when low
ESR (<100mΩ) ceramic capacitors are used. In general,
low ESR is defined as a resistance that is less than
100mΩ.
X7R and X5R type ceramic capacitors are highly recommended over all other types of capacitors for use with
the AAT2847. For the charge pump section, a 1μF or
greater capacitor is required for the fly (C1 and C2) and
output (COUT) capacitors. The dual LDOs require a 2.2μF
or greater output capacitor. The required input capacitor
(CIN) is 2.2μF or greater.
Ceramic capacitors offer many advantages over their
tantalum and aluminum electrolytic counterparts. A
ceramic capacitor typically has very low ESR, is lowest
cost, has a smaller printed circuit board (PCB) footprint,
and is non-polarized. Low ESR ceramic capacitors maximize charge pump transient response.
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15
DATA SHEET
AAT2847
Four-Channel Backlight Driver with Dual LDOs
Before choosing a particular capacitor, verify the capacitor’s performance with the characteristics illustrated in
the component’s data sheet. Performance verification
will help avoid undesirable component related performance deficiencies.
PCB Layout
To achieve adequate electrical and thermal performance,
careful attention must be given to the PCB layout. In the
worst-case operating condition, the chip must dissipate
considerable power at full load. Adequate heat-sinking
must be achieved to ensure intended operation.
Figures 5 and 6 illustrate an example PCB layout. The
bottom of the package features an exposed metal pad.
The exposed pad acts, thermally, to transfer heat from
the chip and, electrically, as a ground connection.
The junction-to-ambient thermal resistance (θJA) for the
connection can be significantly reduced by following a
couple of important PCB design guidelines. The PCB area
directly underneath the package should be plated so that
the exposed paddle can be mated to the top layer PCB
copper during the reflow process. Multiple copper plated
thru-holes should be used to electrically and thermally
connect the top surface pad area to additional ground
plane(s).
The chip ground is internally connected to both the
exposed pad and to the AGND and PGND pins. It is good
practice to connect the GND pins to the exposed pad
area with traces as shown in Figure 4.
The flying capacitors (C1 and C2), input capacitor (C4),
and output capacitors (C3, C5, and C6) should be connected as close as possible to the IC. In addition to the
external passive components being placed as close as
possible to the IC, all traces connecting the AAT2847
should be as short and wide as possible to minimize path
resistance and potential coupling.
Pin #1
Figure 4: AAT2847 Package Layout.
16
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DATA SHEET
AAT2847
Four-Channel Backlight Driver with Dual LDOs
Evaluation Board Layout
Figure 5: AAT2847 Evaluation Board
Component Side Layout.
Figure 6: AAT2847 Evaluation Board
Solder Side Layout.
Evaluation Board Schematic
DC+
DC+
DC+
1
2
3
1
D1
D2
D3
2
3
1
2
3
D4
J1
J2
J3
R10
6
C4
18
17
D3
19
IN
C1+
PGND
C1-
IN
OUT
7
FBA
R11
EN/SET
16
15
14
EN/SET
C1
13
12
11
C3
C2+
5
LDOB
C2-
4
ENB
10
C6
D4
D1
L DOA
3
LDOB
R13
U1
AAT2847
D2
9
2
8
1
GND
FBB
R14
ENA
20
R12
C2
C5
LDOA
R8
R9
Figure 7: AAT2847 Section Schematic.
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17
DATA SHEET
AAT2847
Four-Channel Backlight Driver with Dual LDOs
J4
R6
EN/SET
3
2
1
R7
DC+
DC+
R1
R3
1
2
3
4
DATA
C8
U2
R2
VDD
GP5
GP4
GP3
VSS
GP0
GP1
GP2
8
7
6
5
PIC12F675
R5
LED7
RED
LIGHT
SW
Figure 8: MCU Section Schematic.
18
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DATA SHEET
AAT2847
Four-Channel Backlight Driver with Dual LDOs
Ordering Information
Low Dropout Regulators
Package
LDOA
LDOB
Marking1
Part Number (Tape and Reel)2
TQFN34-20
TQFN34-20
TQFN34-20
Programmable
2.8V
2.8V
Programmable
1.5V
1.8V
YLXXY
AAT2847IML-EE-T1
AAT2847IML-QG-T1
AAT2847IML-QI-T1
ZDXYY
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.
1. XYY = assembly and date code.
2. Sample stock is generally held on part numbers listed in BOLD.
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19
DATA SHEET
AAT2847
Four-Channel Backlight Driver with Dual LDOs
Package Information1
TQFN34-20
3.00 ± 0.05
0.40 ± 0.100
1.55 ± 0.05
2.55 ± 0.05
0.50 BSC
0.24 ± 0.060
4.00 ± 0.05
Detail "A"
Top View
Bottom View
0.75 ± 0.05
Detail "A"
0.025 ± 0.025
Side View
0.214 ± 0.036
All dimensions in millimeters.
1. 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.
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. 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.
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 hereunder, 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, INCLUDING 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 environmental 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 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
design, or damage to any equipment resulting from the use of Skyworks products outside of stated published specifications 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
identification 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.
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