ANALOGICTECH TQFN34-20

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.
•
•
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 current matching is 1% which helps provide uniform
display brightness.
AnalogicTech’s 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.
Typical Application
C1
1μF
•
•
•
•
•
•
•
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
Applications
•
•
•
•
Camera Function Power Supplies
Camera Phone Displays
LCD Modules
White LED Backlighting
C2
1μF
C1- C1+ C2-
ChargePump™
C1
1μF
C2
1μF
C2+
C1- C1+ C2-
OUT
WLEDs
OSRAM LW M673
or equivalent
C OUT
1μF
IN
VBAT
3.6V
D2
D3
D4
IN
LDOA
D3
D4
IN
LDO A Enable
LDO B Enable
FBA
EN/SET
ENA
LDOB
FBB
GND
2847.2007.09.1.0
200mA
C LDOB
2.2μF
ENB
D1
D2
CIN
2.2μF
200mA
C LDOA
2.2μF
AS2Cwire
Backlight Control
WLEDs
OSRAM LW M673
or equivalent
AAT 2847-QI
D1
C IN
2.2μF
C OUT
1μF
IN
AAT 2847-EE
VBAT
3.6V
C2+
OUT
AS2Cwire
Backlight control
LDO A Enable
ENA
LDO B Enable
ENB
VOUTA
2.8V, 200mA
LDOA
CLDOA
2.2μF
EN/SET
VOUTB
1.8V, 200mA
LDOB
CLDOB
2.2μF
GND
PGND
PGND
1
AAT2847
Four-Channel Backlight Driver with Dual LDOs
Pin Descriptions
Symbol
Pin #
AAT2847-EE
AAT2847-QG/QI
1
D2
D2
LED2 current channel input. Connect to the cathode of backlight LED 2. If not
used, connect D2 to the OUT pin.
2
D1
D1
LED1 current channel input. Connect to the cathode of backlight LED 1. If not
used, connect D1 to the OUT pin.
3
LDOB
LDOB
4, 6
IN
IN
5
PGND
PGND
7
FBA
NC
8
9
10
LDOA
C2C2+
LDOA
C2C2+
11
OUT
OUT
12
13
14
C1C1+
EN/SET
C1C1+
EN/SET
15
ENB
ENB
16
D4
D4
17
D3
D3
18
19
GND
ENA
GND
ENA
20
FBB
N/C
EP
2
Function
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).
2847.2007.09.1.0
AAT2847
Four-Channel Backlight Driver with Dual LDOs
Pin Configuration
AAT2847-EE
TQFN34-20
(Top View)
AAT2847-QG/QI
TQFN34-20
(Top View)
D3
GND
ENA
N/C
D3
GND
ENA
FBB
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
D2
D1
LDOB
IN
PGND
IN
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
Absolute Maximum Ratings1
TA = 25°C, unless otherwise noted. Pin descriptions below apply to AAT2847-EE (AAT2847-QG/QI)
Symbol
Description
VN
[IN, OUT, D1, D2, D3, D4] to GND
VN
[C1+, C1-, C2+, C2-] to GND
VN
[LDOA, LDOB, FBA, FBB, EN/SET, ENA, ENB] to GND
TJ
Operating Temperature Range
TLEAD
Maximum Soldering Temperature (at leads, 10 sec)
Value
Units
-0.3 to 6.0
-0.3 to VOUT + 0.3
V
V
-0.3 to VIN + 0.3
V
-40 to 150
°C
300
°C
Value
Units
Thermal Information2, 3
Symbol
Description
θJA
Thermal Resistance
50
°C/W
PD
Maximum Power Dissipation
2
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.
2847.2007.09.1.0
3
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 Units
Power Supply
VIN
ISHDN
Input Voltage Range
Total Shutdown Current at IN
5.5
V
VEN/SET = VENA = VENB = 0V
2.7
1.0
µA
1x Mode, 3.0 ≤ VIN ≤ 5.5, Active, No Load,
VENA = VENB = 0V
1.0
1.5x Mode, 3.0 ≤ VIN ≤ 5.5, Active, No
Load, VENA = VENB = 0V
4.0
2x Mode, 3.0 ≤ VIN ≤ 5.5, Active, No Load,
VENA = VENB = 0V
5.0
Charge Pump
IIN
IDX
I(D-Match)
Input Operating Current
Average Current Accuracy
Current Matching
2
DATA 1, 20mA Range
18
20
22
DATA 2, ADDRESS 4
0.9
1.0
1.1
DATA 1, 30mA Range
30
DATA 1, 15mA Range
VIN - VF = 1.5V, 20mA Range
15
VTH
1x to 1.5x or 1.5x to 2x Transition
20mA Range
Threshold at Any DX Pin
fCLK
Clock Frequency
TSD
THYS
0.5
1
mA
mA
%
150
mV
1
MHz
Over-Temperature Shutdown
Threshold
140
˚C
Over-Temperature Shutdown
Hysteresis
15
˚C
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
0.3
75
µs
75
µs
50
ns
TOFF
EN/SET Off Timeout
500
µs
TLAT
EN/SET Latch Timeout
500
µs
VIL(EN/SET)
EN/SET Logic Low Threshold
Voltage
0.4
V
VIH(EN/SET)
EN/SET Logic High Threshold
Voltage
IEN/SET
EN/SET Input Leakage
1.4
VEN/SET = VIN = 5V
-1
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. 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
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 Units
VENA = VENB = VIN, VEN/SET = 0V, No Load
80
150
VENA = VIN; VENB = 0V; VEN/SET = 0V; No Load
60
112
LDOs: AAT2847-EE
IIN
VFBA, VFBB
IN Operating Current
µA
Feedback Voltage
ILDO[A/B] = 1mA to 200mA
1.2
1.23
V
VDO
Dropout Voltage
ILDO[A/B] = 150mA
150
300
mV
ΔVOUT/
VOUT*ΔVIN
Line Regulation
VIN = (VLDO[A/B] + 1V) to 5V
0.09
%/V
50
dB
PSRR
1.17
Power Supply Rejection
ILDO[A/B] =10mA, 1kHz
Ratio
LDOs: AAT2847-QG
IIN
LDOA
LDOB
VDO
VENA = VENB = VIN, VEN/SET = 0V, No Load
IN Operating Current
LDOA Dropout Voltage
2
ΔVLDO[A/B]/
LDOA, LDOB Line
VLDO[A/B]*ΔVIN Regulation
PSRR
80
150
2.716
60
2.8
112
2.884
1.455
1.5
1.545
V
ILDOA = 150mA
150
300
mV
VIN = (LDOA + 1V) to 5V; VIN = (LDOB + 1.2V)
to 5V
0.09
%/V
ILDO[A/B] =10mA, 1kHz
50
dB
VENA = VENB = VIN, VEN/SET = 0V, No Load
80
150
VENA = VIN; VENB = 0V; VEN/SET = 0V; No Load
60
112
2.716
2.8
2.884
1.746
1.8
1.854
V
150
300
mV
VENA = VIN; VENB = 0V; VEN/SET = 0V; No Load
LDOA Voltage Tolerance ILDOA = 1mA to 150mA
LDOB Voltage Tolerance ILDOB = 1mA to 150mA
LDOA, LDOB Power
Supply Rejection Ratio
µA
V
LDOs: AAT2847-QI
IIN
LDOA
LDOB
VDO
IN Operating Current
LDOA Voltage Tolerance ILDOA = 1mA to 150mA
LDOB Voltage Tolerance ILDOB = 1mA to 150mA
LDOA Dropout Voltage2 ILDOA = 150mA
ΔVLDO[A/B]/
LDOA, LDOB Line
VLDO[A/B]*ΔVIN Regulation
PSRR
LDOA, LDOB Power
Supply Rejection Ratio
VIN = (LDO[A/B] + 1V) to 5V
ILDO[A/B] =10mA, 1kHz
µA
V
0.09
%/V
50
dB
LDO Logic Control – All Options
VIL(ENA),
VIL(ENB)
ENA, ENB Input Logic
Low Threshold Voltage
VIH(ENA),
VIH(ENB)
ENA, ENB Input Logic
High Threshold Voltage
IEN[A/B]
ENA, ENB Input
Leakage
0.4
1.4
VEN[A/B] = VIN = 5V
-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.
2847.2007.09.1.0
5
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
14.5mA/Channel
40
30
2.7
3.1
3.5
3.9
4.3
4.7
5.1
19
-15
10
35
60
85
Temperature (°C)
EN/SET Latch Timeout vs. Input Voltage
EN/SET Off Timeout vs. Input Voltage
400
-40°C
350
-40°C
300
250
TOFF (µs)
TLAT (µs)
19.5
Input Voltage (V)
300
200
150
25°C
85°C
100
250
200
150
2.7
3.1
3.5
3.9
4.3
4.7
5.1
50
2.7
5.5
25°C
85°C
100
50
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
1.2
5.5
1.2
-40°C
1.1
VIL(ENA/ENB), VIL(EN/SET) (V)
VIH(ENA/ENB), VIH(EN/SET) (V)
20
18.5
-40
5.5
350
1.0
0.9
0.8
0.7
0.6
25°C
0.5
85°C
0.4
0.3
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
0.2
2.7
3.1
3.5
3.9
4.3
Input Voltage (V)
6
20.5
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)
2847.2007.09.1.0
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
85°C
25°C
5
VDX
(20mA/div)
0
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
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
(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
7
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)
LDOA/LDOB Line Regulation
1.0
0.5
Output Voltage Error (%)
Output Voltage Error (%)
LDOA/LDOB Load Regulation
LDOA
0.0
-0.5
LDOB
-1.0
0.500
LDOA
0.000
LDOB
-0.500
-1.000
0.1
1
10
Load Current (mA)
8
1.000
100
1000
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
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
(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
VLDOA
(100mV/div)
40
-40°C
20
0
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
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)
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9
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)
2847.2007.09.1.0
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 (D1D4) 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
2847.2007.09.1.0
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.
11
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 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.
30.0
LED Current (mA)
25.0
20.0
15.0
10.0
Address 0
Address 4
5.0
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
AS2Cwire Serial Interface Addressing
Each white LED channel input on the AAT2847
(D1-D4) is controlled by AnalogicTech's 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.
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.
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.
A typical write protocol consist of the following:
First a burst of EN/SET rising edges that
Address
Data
T HI
T LO
TLAT
TLAT
EN/SET
1
Address
2
19
20
1
0
2...
n ≤ 16
3
DATA3
1
DATA0
1
n
Figure 2: AS2Cwire 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 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.
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 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.
Data
Current Scale
1
2
3
4
20mA Scale
30mA Scale
15mA Scale
Low Current Mode
Table 3: Current Scale Settings—Address 3.
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.
2847.2007.09.1.0
13
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.
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.
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.
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.
14
2847.2007.09.1.0
AAT2847
Four-Channel Backlight Driver with Dual LDOs
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:
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.
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.
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=
η=
PLEDs VLED1 · ILED1 + ... + VLED4 · ILED4
=
PIN
VIN · IIN
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:
Device Power Efficiency
η=
PLEDs VLED1 · ILED1 + ... + VLED4 · ILED4
=
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:
η=
4 · VLEDX · ILEDX
; x = 1, 2, 3 or 4 and IIN = 2(4 · ILEDX)
VIN · IIN
V
·I
+ ... + VLED4 · ILED4
P
η = LEDs = LED1 LED1
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
2847.2007.09.1.0
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
15
AAT2847
Four-Channel Backlight Driver with Dual LDOs
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.
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
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
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
15
14
EN/SET
C1
13
12
11
C3
C2+
5
LDOB
16
10
4
ENB
C2-
C6
D4
D1
9
3
LDOB
R13
U1
AAT2847
D2
L DOA
2
8
1
GND
FBB
R14
ENA
20
R12
C2
C5
LDOA
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
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
2847.2007.09.1.0
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
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
Package Information1
TQFN34-20
3.00 ± 0.05
1.55 ± 0.05
2.55 ± 0.05
4.00 ± 0.05
Detail "A"
Top View
Bottom View
0.425 ± 0.05
0.75 ± 0.05
7.5° ± 7.5°
0.021 ± 0.004
0.5 BSC
Side View
0.23 ± 0.06
0.025 ± 0.025
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 without notice. Except as provided in AnalogicTech’s terms and conditions of sale, AnalogicTech assumes no liability whatsoever, and AnalogicTech disclaims any express or implied warranty 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.
Advanced Analogic Technologies, Inc.
3230 Scott Boulevard, Santa Clara, CA 95054
Phone (408) 737-4600
Fax (408) 737-4611
20
2847.2007.09.1.0