AAT2847IML-QG-T1 [ANALOGICTECH]
Four-Channel Backlight Driver with Dual LDOs; 四通道背光驱动器，带有双LDO
| 型号： | AAT2847IML-QG-T1 |
| 厂家： | 
ADVANCED ANALOGIC TECHNOLOGIES |
| 描述： | Four-Channel Backlight Driver with Dual LDOs |
| 文件： | 总20页 (文件大小：382K) |
| 中文： | 中文翻译 | 下载： | 下载PDF数据表文档文件 |
AAT2847
Four-Channel Backlight Driver with Dual LDOs
™
ChargePump
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 volt-
age regulators (LDOs) as additional power sup-
plies 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
The backlight driver in the AAT2847 is a low noise
tri-mode 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 cur-
rent matching is 1% which helps provide uniform
display brightness.
•
— Dual 200mA LDOs (w/Separate Enables)
2
•
Single-Wire AS Cwire Serial Interface for
Configuration/Control
2
AnalogicTech’s AS Cwire™ (Advanced Simple
— Four Addressable Registers
— Fast, 1MHz Serial Interface
> 90% Peak Efficiency
Serial Control™) serial digital interface is used to
enable, disable, and set the current for each back-
light LED channel. Each LED channel has sixteen
available current level settings in three separate
current scales, plus four available current level set-
tings on a low level current scale.
•
•
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
•
•
•
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.
Applications
The AAT2847 is available in the thermally
enhanced 20-pin 3x4x0.75mm TQFN package.
•
•
•
•
Camera Function Power Supplies
Camera Phone Displays
LCD Modules
White LED Backlighting
Typical Application
C1
1μF
C2
1μF
C1
1μF
C2
1μF
C1- C1+ C2- C2+
OUT
C1- C1+ C2- C2+
OUT
WLEDs
WLEDs
OSRAM LW M673
OSRAM LW M673
or equivalent
COUT
1μF
or equivalent
COUT
1μF
IN
IN
AAT 2847-EE
AAT2847-QI
VBAT
3.6V
D1
D2
D3
D4
VBAT
3.6V
D1
D2
D3
D4
CIN
2.2μF
CIN
2.2μF
200mA
VOUTA
IN
LDOA
IN
LDOA
2.8V, 200mA
CLDOA
2.2μF
AS2Cwire
Backlight control
CLDOA
2.2μF
EN/SET
FBA
AS2Cwire
EN/SET
ENA
ENB
LDO A Enable
LDO B Enable
Backlight Control
LDO A Enable
LDO B Enable
200mA
VOUTB
1.8V, 200mA
LDOB
PGND
LDOB
ENA
ENB
CLDOB
2.2μF
CLDOB
2.2μF
GND
FBB
GND
PGND
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AAT2847
Four-Channel Backlight Driver with Dual LDOs
Pin Descriptions
Symbol
Pin #
Function
AAT2847-EE AAT2847-QG/QI
LED2 current channel input. Connect to the cathode of backlight LED 2. If not
used, connect D2 to the OUT pin.
1
D2
D1
D2
D1
LED1 current channel input. Connect to the cathode of backlight LED 1. If not
used, connect D1 to the OUT pin.
2
3
4, 6
5
LDOB
IN
LDOB
IN
Output of LDOB.
Input voltage supply connection.
PGND
PGND
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.
7
FBA
NC
8
9
LDOA
C2-
LDOA
C2-
Negative terminal of flying capacitor 2.
10
C2+
C2+
Positive terminal of flying capacitor 2.
Charge pump output to drive load circuit. Connect a 1µF or larger ceramic
capacitor between OUT and PGND.
11
OUT
OUT
12
13
14
15
C1-
C1+
EN/SET
ENB
C1-
C1+
EN/SET
ENB
Negative terminal of flying capacitor 1.
Positive terminal of flying capacitor 1.
2
AS Cwire 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.
16
D4
D4
LED3 current channel input. Connect to the cathode of backlight LED 3. If not
used, connect D3 to the OUT pin.
17
D3
D3
18
19
GND
ENA
GND
ENA
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).
20
FBB
N/C
EP
2
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AAT2847
Four-Channel Backlight Driver with Dual LDOs
Pin Configuration
AAT2847-EE
TQFN34-20
(Top View)
AAT2847-QG/QI
TQFN34-20
(Top View)
1
2
3
4
5
6
16
15
14
13
12
11
1
2
3
4
5
6
16
D2
D1
LDOB
IN
PGND
IN
D4
D2
D1
LDOB
IN
PGND
IN
D4
15
14
13
12
11
ENB
EN/SET
C1+
C1-
OUT
ENB
EN/SET
C1+
C1-
OUT
1
Absolute Maximum Ratings
TA = 25°C, unless otherwise noted. Pin descriptions below apply to AAT2847-EE (AAT2847-QG/QI)
Symbol Description
Value
Units
VN
VN
[IN, OUT, D1, D2, D3, D4] to GND
[C1+, C1-, C2+, C2-] to GND
-0.3 to 6.0
-0.3 to VOUT + 0.3
V
V
VN
-0.3 to VIN + 0.3
[LDOA, LDOB, FBA, FBB, EN/SET, ENA, ENB] to GND
Operating Temperature Range
V
TJ
-40 to 150
300
°C
°C
TLEAD
Maximum Soldering Temperature (at leads, 10 sec)
2, 3
Thermal Information
Symbol Description
Value
Units
θJA
PD
Thermal Resistance
Maximum Power Dissipation
50
2
°C/W
W
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.
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AAT2847
Four-Channel Backlight Driver with Dual LDOs
1
Electrical Characteristics
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
Conditions
Min Typ Max Units
VIN
ISHDN
Input Voltage Range
Total Shutdown Current at IN
2.7
5.5
1.0
V
µA
VEN/SET = VENA = VENB = 0V
Charge Pump
1x Mode, 3.0 ≤ VIN ≤ 5.5, Active, No Load,
1.0
4.0
5.0
VENA = VENB = 0V
1.5x Mode, 3.0 ≤ VIN ≤ 5.5, Active, No
Load, VENA = VENB = 0V
IIN
Input Operating Current
mA
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
18
0.9 1.0
20
22
1.1
IDX
Average Current Accuracy
mA
30
15
0.5
2
I(D-Match)
VTH
Current Matching
1
%
mV
MHz
˚C
1x to 1.5x or 1.5x to 2x Transition
Threshold at Any DX Pin
Clock Frequency
20mA Range
150
1
fCLK
Over-Temperature Shutdown
Threshold
TSD
140
Over-Temperature Shutdown
Hysteresis
THYS
15
˚C
EN/SET Logic Control
TEN/SET LO
TEN/SET_HI_MIN
TEN/SET_HI_MAX
TOFF
EN/SET Low Time
0.3
50
75
µs
ns
µs
µs
µs
Minimum EN/SET High Time
Maximum EN/SET High Time
EN/SET Off Timeout
75
500
500
TLAT
EN/SET Latch Timeout
EN/SET Logic Low Threshold
Voltage
VIL(EN/SET)
0.4
1
V
EN/SET Logic High Threshold
Voltage
VIH(EN/SET)
IEN/SET
1.4
-1
V
VEN/SET = VIN = 5V
EN/SET Input Leakage
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
2847.2007.09.1.0
AAT2847
Four-Channel Backlight Driver with Dual LDOs
1
Electrical Characteristics
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 Units
LDOs: AAT2847-EE
VENA = VENB = VIN, VEN/SET = 0V, No Load
VENA = VIN; VENB = 0V; VEN/SET = 0V; No Load
ILDO[A/B] = 1mA to 200mA
80
60
150
112
IIN
IN Operating Current
µA
VFBA, VFBB
VDO
Feedback Voltage
Dropout Voltage
1.17
1.2 1.23
150 300
V
mV
ILDO[A/B] = 150mA
ΔVOUT
OUT*ΔVIN
/
VIN = (VLDO[A/B] + 1V) to 5V
ILDO[A/B] =10mA, 1kHz
Line Regulation
0.09
50
%/V
dB
V
Power Supply Rejection
Ratio
PSRR
LDOs: AAT2847-QG
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
80
60
150
112
IIN
IN Operating Current
µA
LDOA
LDOB
VDO
LDOA Voltage Tolerance
LDOB Voltage Tolerance
LDOA Dropout Voltage
2.716 2.8 2.884
1.455 1.5 1.545
150 300
V
V
mV
2
ΔVLDO[A/B]
LDO[A/B]*ΔVIN
/
LDOA, LDOB Line
Regulation
VIN = (LDOA + 1V) to 5V; VIN = (LDOB + 1.2V)
to 5V
0.09
50
%/V
dB
V
LDOA, LDOB Power
Supply Rejection Ratio
ILDO[A/B] =10mA, 1kHz
PSRR
LDOs: AAT2847-QI
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
80
60
150
112
IIN
IN Operating Current
µA
LDOA
LDOB
VDO
LDOA Voltage Tolerance
LDOB Voltage Tolerance
LDOA Dropout Voltage
2.716 2.8 2.884
1.746 1.8 1.854
150 300
V
V
mV
2
ΔVLDO[A/B]
LDO[A/B]*ΔVIN
/
LDOA, LDOB Line
Regulation
VIN = (LDO[A/B] + 1V) to 5V
ILDO[A/B] =10mA, 1kHz
0.09
50
%/V
dB
V
LDOA, LDOB Power
Supply Rejection Ratio
PSRR
LDO Logic Control – All Options
VIL(ENA)
VIL(ENB)
,
ENA, ENB Input Logic
Low Threshold Voltage
0.4
V
V
VIH(ENA)
VIH(ENB)
,
ENA, ENB Input Logic
High Threshold Voltage
1.4
-1
ENA, ENB Input
Leakage
IEN[A/B]
VEN[A/B] = VIN = 5V
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.
2847.2007.09.1.0
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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
90
80
70
60
50
40
30
21
20.5
20
20mA/Channel
19.5
19
1mA/Channel
14.5mA/Channel
18.5
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
-40
-15
10
35
60
85
Input Voltage (V)
Temperature (°C)
EN/SET Latch Timeout vs. Input Voltage
EN/SET Off Timeout vs. Input Voltage
400
350
300
250
200
150
100
50
350
300
250
200
150
100
50
-40°C
-40°C
25°C
85°C
25°C
85°C
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
Input Voltage (V)
Logic High Threshold Voltage
vs. Input Voltage
Logic Low Threshold Voltage
vs. Input Voltage
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
1.2
1.1
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
-40°C
-40°C
85°C
25°C
85°C
25°C
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
Input Voltage (V)
6
2847.2007.09.1.0
AAT2847
Four-Channel Backlight Driver with Dual LDOs
Typical Characteristics
Shutdown Current vs. Input Voltage
(VEN/SET = VENA/ENB = 0V)
Backlight Operating Characteristic
(VIN = 3.7V; 1.5X Mode; 20mA/Channel Load;
AC Coupled)
20
VIN
(20mV/div)
-40°C
15
VOUT
(40mV/div)
10
85°C
25°C
5
0
VDX
(20mA/div)
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
Time (500ns/div)
Backlight Operating Characteristic
(VIN = 3.5V; 1.5X Mode; 14mA/Channel Load;
AC Coupled)
Backlight Operating Characteristic
(VIN = 2.9V; 2X Mode; 20mA/Channel Load;
AC Coupled)
VIN
(20mV/div)
VIN
(20mV/div)
VOUT
(40mV/div)
VOUT
(40mV/div)
VDX
(20mA/div)
VDX
(40mA/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
(40mA/div)
Time (500ns/div)
2847.2007.09.1.0
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AAT2847
Four-Channel Backlight Driver with Dual LDOs
Typical Characteristics
Turn On to 1X Mode Backlight
(20mA/Channel; Address 0, Data 1; VIN = 4.2V)
Turn On to 1.5X Mode Backlight
(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 (500ns/div)
Time (200µs/div)
Turn On to 2X Mode Backlight
(20mA/Channel; Address 0, Data 1; VIN = 3.2V)
Turn Off from 1.5X Mode Backlight
(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)
LDOA/LDOB Load Regulation
LDOA/LDOB Line Regulation
1.0
0.5
1.000
0.500
0.000
-0.500
LDOA
LDOB
LDOA
LDOB
0.0
-0.5
-1.0
0.1
-1.000
2.7
1
10
100
1000
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Load Current (mA)
Input Voltage (V)
8
2847.2007.09.1.0
AAT2847
Four-Channel Backlight Driver with Dual LDOs
Typical Characteristics
LDOA/LDOB Quiescent Current vs. Input Voltage
LDOA Load Transient Response
(VIN = 3.6V; VLDOA = 1.2V)
(VOUT = 1.2V)
120
200mA
85°C
25°C
100
80
60
40
20
0
ILDOA
(100mA/div)
10mA
VLDOA
(100mV/div)
-40°C
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
Time (20µs/div)
LDOB Load Transient Response
(VIN = 3.6V; VLDOB = 1.2V)
LDOA Line Transient Response
(10mA Load)
200mA
VIN = 4.2V
ILDOB
(100mA/div)
VIN
(400mV/div)
10mA
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)
2847.2007.09.1.0
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AAT2847
Four-Channel Backlight Driver with Dual LDOs
Typical Characteristics
LDOA/LDOB Turn On
(VIN = 3.6V; VLDO(A/B) = 2.8V; DC Coupled)
LDOA/LDOB Turn On
(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
(VIN = 3.6V; VLDO(A/B) = 1.5V; DC Coupled)
LDOA/LDOB Turn On
(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)
Time (40µs/div)
10
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AAT2847
Four-Channel Backlight Driver with Dual LDOs
Functional Block Diagram
C1+ C1- C2+ C2-
Tri-Mode
AAT2847-EE
(AAT 2847-QG/-QI)
(1x, 1.5x and 2x)
OUT
IN
Charge Pump
1.2V
Reference
1MHz
Oscillator
Voltage
Reference
D/A
D/A
D/A
D1
D2
D3
AS2Cwire
Interface
6 x16 bit
ROM
EN/SET
D/A
D4
IN
LDOA (2.8V/2.8V)
FBA (NC)
LDO A
LDO B
ENA
LDOB (1.5V/1.8V)
FBB (NC)
ENB
(AAT 2847-QG/-QI)
GND
PGND
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.
Functional Description
The AAT2847 is an integrated solution for LCD dis-
play 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) func-
tionality and high efficiency (1.5X or 2X) perform-
ance. 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 thresh-
old for 1X to 1.5X and 1.5X to 2X mode transitions
is VTH.
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
2
significant reduction in efficiency. The AS Cwire
serial interface enables the charge pump and sets
the current flowing into the LED cathode input pins.
The AAT2847 also contains dual LDO voltage reg-
ulators 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.
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
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AAT2847
Four-Channel Backlight Driver with Dual LDOs
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 sig-
nify data with the accompanying TLAT timeout peri-
od to latch the data value in the data register. Once
an address is set, then multiple writes to the corre-
30.0
25.0
20.0
15.0
10.0
5.0
Address 0
Address 4
sponding 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
0.0
1
2
3
4
5
6
7
8
9
10 11 12 13 14 15 16
1
2
3
4
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.
Code
Figure 1: LED Current Control Profile.
2
AS Cwire Serial Interface
2
AS Cwire Serial Interface Addressing
Each white LED channel input on the AAT2847
2
(D1-D4) is controlled by AnalogicTech's AS Cwire
EN/SET
2
serial digital interface. The AS Cwire interface uses
Address Edges
Addressed Register
D1-D4 Current Control
Current Scale
Low Current Control
Independent LED Control
the number of rising edges on the EN/SET pin to
address and load the LED configuration registers.
0
3
4
5
17
20
21
22
2
AS Cwire latches data or addresses after the
EN/SET pin has been held logic high for longer
than TLAT (500µs). Addresses and data are differ-
entiated by the number of EN/SET rising edges.
Since the data registers are 4 bits each, the differ-
2
Table 1: AS Cwire Serial Interface Addressing.
4
entiating number of pulses is 2 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.
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 cur-
rent level by writing to Address 0 followed by any
Data between, and including, 1 to 16.
A typical write protocol consist of the following:
First a burst of EN/SET rising edges that
Address
THI
Data
TLAT
TLO
TLAT
EN/SET
1
2
19
0
20
1
2 . . .
n ≤ 16
Address
DATA3
DATA0
3
1
1
n
2
Figure 2: AS Cwire Serial Interface Timing.
12
2847.2007.09.1.0
AAT2847
Four-Channel Backlight Driver with Dual LDOs
Current Scale (Address 3)
Low Current Operation (Address 4)
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 toAddress 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 cur-
rent set by the low current settings in 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 oper-
ational mode is especially useful for low current
applications where a continuous low current state
is maintained for a substantial length of time.
Data
mA
0.5
1.0
1.5
2.0
1
2
3
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
20.0
19.0
17.7
16.8
15.5
14.5
13.2
12.3
11.0
10.0
8.7
15.0
14.3
13.3
12.6
11.6
10.9
9.9
9.2
8.3
7.5
6.5
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 independ-
ent control write Address 5 with Data between, and
including, 1 to 16.
Data
D4
D3
D2
D1
7.7
6.5
5.5
4.2
5.8
4.9
4.1
3.2
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
8.3
6.3
4.8
3.2
2.4
Table 2: Current Settings—Address 0.
Data
Current Scale
20mA Scale
30mA Scale
15mA Scale
Low Current Mode
1
2
3
4
Table 3: Current Scale Settings—Address 3.
Table 5: Independent LED Control Settings—
Address 5.
2847.2007.09.1.0
13
AAT2847
Four-Channel Backlight Driver with Dual LDOs
Auto Disable Feature
Applications Information
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.
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 for-
ward voltage specifications ranging from 2.0V to
4.7V. LED applications may include mixed arrange-
ments 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 com-
bined to obtain a higher LED drive current without
complication.
Low Dropout Regulators
The AAT2847 incorporates two LDO voltage regu-
lators. 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 out-
put (LDOA or LDOB) to the feedback input (FBA or
FBB). The ratio of the voltage divider resistor val-
ues 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.
AAT2847-EE LDO Output Voltage
Programming
The output voltages for LDOA and LDOB are pro-
grammed 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 consider-
ing 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.
Thermal Protection
LDO(A/B)
FB(A/B)
VLDO(A/B)
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.
R2(A/B)
R1(A/B)
VREF = 1.2V
Figure 3: Selection of External Resistors.
To select appropriate resistor values, first choose a
value for R1 that will produce a reasonable feed-
back network bias current. Then, according to the
desired VLDO(A/B), calculate R2 according to the
equation below. An example calculation follows.
14
2847.2007.09.1.0
AAT2847
Four-Channel Backlight Driver with Dual LDOs
R1 is chosen to be 120kΩ, resulting in a small
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.
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:
R1(A/B)(VLDO(A/B) - 1.2V)
1.2V
R2(A/B)
=
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:
The result is R2 = 60kΩ. Since 60kΩ is not a stan-
dard 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 pro-
vided below.
PLEDs VLED1 · ILED1 + ... + VLED4 · ILED4
=
η =
PIN
VIN · IIN
4 · VLEDX · ILEDX
VIN · IIN
R2 Standard 1% Values (R1 = 120kΩ)
η =
η =
; x = 1, 2, 3 or 4 and IIN = 1.5(4 · ILEDX)
VLDO(A/B) (V)
R2 (Ω)
160k
130k
79.6k
60.4k
30.1k
VLEDX
1.5VIN
2.8
2.5
2
1.8
1.5
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:
Table 6: Example Output Voltages and
Corresponding Resistor Values.
PLEDs VLED1 · ILED1 + ... + VLED4 · ILED4
=
η =
Device Power Efficiency
PIN
VIN · IIN
The AAT2847’s charge pump conversion efficiency
is defined as the power delivered to the white LED
load divided by the input power:
4 · VLEDX · ILEDX
VIN · IIN
η =
η =
; x = 1, 2, 3 or 4 and IIN = 2(4 · ILEDX)
VLEDX
2VIN
PLEDs VLED1 · ILED1 + ... + VLED4 · ILED4
=
η =
PIN
VIN · IIN
Capacitor Selection
VLEDx = White LED Forward Voltage (VF)
ILEDx = White LED Bias Current (ID)
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.
The expression to define the estimated ideal effi-
ciency (η) for the AAT2847 in 1X mode is as follows:
PLEDs VLED1 · ILED1 + ... + VLED4 · ILED4
=
η =
PIN
VIN · IIN
4 · VLEDX · ILEDX
VIN · IIN
X7R and X5R type ceramic capacitors are highly
recommended over all other types of capacitors for
use with the AAT2847. For the charge pump sec-
tion, a 1µF or greater capacitor is required for the fly
(C1 and C2) and output (COUT) capacitors. The dual
η =
η =
; x = 1, 2, 3 or 4 and IIN = 4 · ILEDX
VLEDX
VIN
2847.2007.09.1.0
15
AAT2847
Four-Channel Backlight Driver with Dual LDOs
LDOs require a 2.2µF or greater output capacitor.
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 required input capacitor (CIN) is 2.2µF or
greater.
Ceramic capacitors offer many advantages over
their tantalum and aluminum electrolytic counter-
parts. 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.
The junction-to-ambient thermal resistance (θJA) for
the connection can be significantly reduced by fol-
lowing 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).
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.
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.
PCB Layout
To achieve adequate electrical and thermal per-
formance, 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.
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 addi-
tion 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.
Figure 4: AAT2847 Package Layout.
16
2847.2007.09.1.0
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
2
3
1
2
3
D1
D2
D3
D4
J1
J3
J2
R12
R13
U1
AAT2847
R14
1
2
3
4
5
6
16
15
14
13
12
11
D2
D1
D4
ENB
LDOB
LDOB
IN
EN/SET
C1+
EN/SET
C6
C1
PGND
IN
C1-
R10
OUT
C4
R11
C3
C2
LDOA
C5
R8
R9
Figure 7: AAT2847 Section Schematic.
2847.2007.09.1.0
17
AAT2847
Four-Channel Backlight Driver with Dual LDOs
J4
R6
EN/SET
3
2
1
R7
DC+
DC+
R1
R3
C8
R2
U2
R5
1
2
3
4
8
7
6
5
VDD
VSS
GP0
GP1
GP2
GP5
GP4
GP3
DATA
LED7
RED
PIC12F675
LIGHT
SW
Figure 8: MCU Section Schematic.
18
2847.2007.09.1.0
AAT2847
Four-Channel Backlight Driver with Dual LDOs
Ordering Information
Low Dropout Regulators
1
2
Package
Marking
YLXXY
Part Number (Tape and Reel)
LDOA
Programmable
2.8V
LDOB
Programmable
1.5V
TQFN34-20
TQFN34-20
TQFN34-20
AAT2847IML-EE-T1
AAT2847IML-QG-T1
AAT2847IML-QI-T1
2.8V
1.8V
ZDXYY
All AnalogicTech products are offered in Pb-free packaging. The term “Pb-free” means
semiconductor products that are in compliance with current RoHS standards, including
the requirement that lead not exceed 0.1% by weight in homogeneous materials. For more
information, please visit our website at http://www.analogictech.com/pbfree.
1. XYY = assembly and date code.
2. Sample stock is generally held on part numbers listed in BOLD.
2847.2007.09.1.0
19
AAT2847
Four-Channel Backlight Driver with Dual LDOs
1
Package Information
TQFN34-20
3.00 0.05
1.55 0.05
Detail "A"
Top View
Bottom View
0.425 0.05
7.5° 7.5°
0.025 0.025
0.021 0.004
Side View
Detail "A"
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.
© Advanced Analogic Technologies, Inc.
AnalogicTech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an AnalogicTech product. No circuit patent licenses, copyrights, mask work
rights, or other intellectual property rights are implied. AnalogicTech reserves the right to make changes to their products or specifications or to discontinue any product or service with-
out notice. Except as provided in AnalogicTech’s terms and conditions of sale, AnalogicTech assumes no liability whatsoever, and AnalogicTech disclaims any express or implied war-
ranty relating to the sale and/or use of AnalogicTech products including liability or warranties relating to fitness for a particular purpose, merchantability, or infringement of any patent,
copyright or other intellectual property right. In order to minimize risks associated with the customer’s applications, adequate design and operating safeguards must be provided by the
customer to minimize inherent or procedural hazards. Testing and other quality control techniques are utilized to the extent AnalogicTech deems necessary to support this warranty.
Specific testing of all parameters of each device is not necessarily performed. AnalogicTech and the AnalogicTech logo are trademarks of Advanced Analogic Technologies Incorporated.
All other brand and product names appearing in this document are registered trademarks or trademarks of their respective holders.
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Phone (408) 737-4600
Fax (408) 737-4611
20
2847.2007.09.1.0
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