AAT AAT2803

AAT2803
Six-Channel White LED Backlight
Charge Pump with Flash
General Description
Features
The AAT2803 is a dual charge pump designed to support both white LED backlight and flash applications
for systems operating with lithium-ion/polymer batteries. The backlight charge pump is capable of driving
up to six LEDs at a total of 180mA. The current sinks
may be operated in group or in parallel for driving
higher current LEDs. To maximize power efficiency,
the charge pump operates in 1X, 1.5X, or 2X mode,
where the mode of operation is automatically selected by comparing the forward voltage of each LED
with the input voltage. AnalogicTech's AS2Cwire™
(Advanced Simple Serial Control™) serial digital input
is used to enable, disable, and set current for each
LED with a 16-level logarithmic scale plus four lowcurrent settings down to 50μA for optimized efficiency, with a low housekeeping current of only 50μA.
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•
VIN Range: 2.7V to 5.5V
Dual Charge Pump:
— Flash: Charge Pump Doubler
— Backlight: Tri-Mode Charge Pump
Backlight Charge Pump:
— Programmable Current With Single GPIO
— 16 Current Steps
— 15/20/30mA Max Current
— Four Low Current Settings
— Individual Main/Sub-Group Control
— Low IQ (50μA) for Low-Current Mode
— Drives Six Channels of LEDs
Flash Charge Pump:
— Regulated VOUT_FL 4.5/5.0 Volts
— Up to 300mA of Current for Flash
1MHz Constant Switching Frequency
Independent Backlight/Flash Control
Built-In Thermal Protection
Built-In Auto-Disable for Open Circuit
Automatic Soft Start
IQ <1μA in Shutdown
Available in QFN44-24 Package
•
•
•
•
•
•
•
•
•
The flash charge pump is a charge pump doubler
with a regulated output voltage. It is designed to
deliver 120mA of continuous current and up to
300mA of pulsed current. It has an independent
enable pin for improved power savings.
The AAT2803 is equipped with built-in protection,
short-circuit, and auto-disable for load short-circuit
condition. Built-in soft-start circuitry prevents excessive inrush current during start-up. A low-current
shutdown feature disconnects the load from VIN and
reduces quiescent current to less than 1μA.
ChargePump™
Applications
•
•
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•
The AAT2803 is available in a Pb-free, space-saving,
thermally enhanced 24-pin 4x4mm QFN package
and is rated over the -40°C to +85°C temperature
range.
Color (RGB) Lighting
Programmable Current Sink
White LED Backlighting
White Photo Flash for Digital Still Cameras
Typical Application
C1
1μF
C1+
VIN
V IN
C2
1μF
C1- C2+
C3
1μF
C2- C3 + C3 VOUT
Flash
COUT
1μF
CIN
1μF
AAT2803
Backlight
D6
EN_FL
EN/SET
ENFL
EN/SET
GND
2803.2006.12.1.6
D5
D4
D3
D2
D1
COUT
1μF
D6
D5
D4
D3
D2
D1
1
AAT2803
Six-Channel White LED Backlight
Charge Pump with Flash
Pin Descriptions
Pin #
Symbol
Function
1
2
3
4, 14
5
C1C1+
VOUT_FL
VIN
EN_FL
6, 7, 23
8
N/C
VOUT_BL
9
10
11
12
13, 15, 24
16
17
18
19
20
21
22
C2+
C3+
C3C2GND
D1
D2
D3
D5
D4
D6
EN/SET
Flying capacitor 1 negative terminal.
Flying capacitor 1 positive terminal. Connect a 1μF capacitor between C1+ and C1-.
Flash output voltage. Requires 1μF capacitor connected between this pin and ground.
Input power supply. Requires 1μF capacitor connected between this pin and ground.
Enable pin for flash charge pump. For normal operation, connect to VIN. When connected low, the flash charge pump shuts down and consumes less than 1μA of current.
No connect.
Backlight output voltage charge pump. Requires 1μF capacitor connected between this
pin and ground.
Flying capacitor 2 positive terminal. Connect a 1μF capacitor between C2+ and C2-.
Flying capacitor 3 positive terminal. Connect a 1μF capacitor between C3+ and C3-.
Flying capacitor 3 negative terminal.
Flying capacitor 2 negative terminal.
Ground.
Current sink input #1.
Current sink input #2.
Current sink input #3.
Current sink input #5.
Current sink input #4.
Current sink input #6.
AS2Cwire serial interface control pin for backlight charge pump. It controls the current
settings for all six channels. This pin should not be left floating.
Exposed paddle (bottom); connect to GND directly beneath package.
EP
Pin Configuration
QFN44-24
(Top View)
D5
D4
D6
EN/SET
N/C
GND
19
20
21
22
23
24
C1C1+
VOUT_FL
VIN
EN_FL
N/C
1
18
2
17
3
16
AAT2803
4
15
5
14
6
13
D3
D2
D1
GND
VIN
GND
12
11
9
10
8
7
C2C3C3+
C2+
VOUT_BL
N/C
2
2803.2006.12.1.6
AAT2803
Six-Channel White LED Backlight
Charge Pump with Flash
Absolute Maximum Ratings1
Symbol
VIN
VEN/SET
TJ
TLEAD
Description
Input Voltage
EN/SET to GND Voltage
Operating Junction Temperature Range
Maximum Soldering Temperature (at leads, 10 sec)
Value
Units
-0.3 to 6
-0.3 to VIN + 0.3
-40 to 150
300
V
V
°C
°C
Value
Units
2.0
50
W
°C/W
Thermal Information2
Symbol
PD
θJA
Description
Maximum Power Dissipation
Maximum Thermal Resistance
3
1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions
other than the operating conditions specified is not implied. Only one Absolute Maximum Rating should be applied at any one time.
2. Mounted on an FR4 board.
3. Derate 6.25mW/°C above 25°C.
2803.2006.12.1.6
3
AAT2803
Six-Channel White LED Backlight
Charge Pump with Flash
Electrical Characteristics1
VIN = 3.6V, CIN = COUT = C1 = C2 = C3 = 1.0μF; TA = -40°C to +85°C, unless otherwise noted.
Typical values are TA = 25°C.
Symbol
VIN
ICC
ISHDN
IDX
I(D-Match)
VTH
VOUT
IOUT
Description
Operation Range
Operating Current
Shutdown Current
ISINK Average Current Accuracy2
Current Matching Between Any
Two Current Sink Inputs3, 4
1X to 1.5X or 1.5X to 2X Transition
Threshold at Any DX Pin
Output Voltage (Flash Charge
Pump)5
Max Continuous Output Current
(Flash Charge Pump)5
Max Pulsed Output Current5
TSS
FCLK
VEN(L)
VEN(H)
Conditions
Soft-Start Time
Clock Frequency
Enable Threshold Low
Enable Threshold High
Min
Typ
2.7
1X Mode, 3.0 ≤ VIN ≤ 5.5, Active,
No Load Current; EN/SET = VIN;
EN_FL= GND
1.5X Mode, 3.0 ≤ VIN ≤ 5.5, Active,
No Load Current; EN/SET = VIN;
EN_FL= GND
2X Mode, 3.0 ≤ VIN ≤ 5.5, Active,
No Load Current; EN/SET = VIN;
EN_FL = GND
VOUT_FLASH = 5V; EN/SET = GND;
EN_FL = VIN
50μA Setting, 1X Mode; EN/SET
= VIN; EN_FL = GND
EN/SET = 0
ISET = 30mA, TA = 25°C
ISET = 4.1mA, TA = 25°C
VF:D1:D4 = 3.6V
Max Units
5.5
0.3
1
1.0
3.0
mA
2.0
3.7
2.0
4.5
50
27
3.69
30
4.1
0.5
μA
1.0
33
4.51
VIN = 2.7V
VIN = 5.5V
4.3
4.5
μA
mA
%
150
3.0< VIN < 5V, IOUT = 120mA;
EN_FL = VIN
VIN = 3.3V; VOUT = 4.5V;
EN_FL = VIN
VIN = 3.6V; VOUT = 4.5V;
IPULSED = 250ms
Backlight Charge Pump
Flash Charge Pump
V
mV
4.7
V
120
mA
300
100
200
1.0
μs
0.4
1.4
MHz
V
V
1. The AAT2803 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured
by design, characterization, and correlation with statistical process controls.
2. Determined by the average of all active channels.
3. Current matching is defined as the deviation of any sink current from the average of all active channels.
4. Specification applies only to the tri-mode charge pump.
5. Specification applies only to the charge pump doubler.
4
2803.2006.12.1.6
AAT2803
Six-Channel White LED Backlight
Charge Pump with Flash
Electrical Characteristics1
VIN = 3.6V, CIN = COUT = C1 = C2 = C3 = 1.0μF; TA = -40°C to +85°C, unless otherwise noted.
Typical values are TA = 25°C.
Symbol
TEN/SET LO
TEN/SET_HI_MIN
TEN/SET_HI_MAX
TOFF
TLAT
IEN/SET;EN_FL
Description
EN/SET Low Time
Minimum EN/SET High Time
Maximum EN/SET High Time
EN/SET Off Timeout
EN/SET Latch Timeout
Input Leakage
Conditions
Min
Typ
0.3
Max Units
75
50
VEN/SET;EN_FL = 5V; VIN = 5V
-1.0
75
500
500
1.0
μs
ns
μs
μs
μs
μA
1. The AAT2803 is guaranteed to meet performance specifications over the -40°C to +85°C operating temperature range and is assured
by design, characterization, and correlation with statistical process controls.
2803.2006.12.1.6
5
AAT2803
Six-Channel White LED Backlight
Charge Pump with Flash
Typical Characteristics–Flash Driver Charge Pump Section
Output Voltage vs. Output Current
Maximum Current Pulse vs. Supply Voltage
(VOUT_FL = 4.5V; EN_FL = VIN; EN/SET = GND)
Output Voltage (V)
4.60
4.56
4.52
3.6V
4.48
3.0V
3.3V
4.44
2.7V
4.40
0.1
1.0
10.0
100.0
1000.0
Maximum Current Pulse (mA)
(VOUT_FL = 4.5V; EN_FL = VIN; EN/SET = GND)
450
400
One-shot pulse duration = 250ms
VOUT > 4.0V
350
300
250
200
150
100
50
0
3.0
3.1
Output Current (mA)
3.2
3.3
3.4
3.6
3.7
3.8
3.9
4.0
4.1
4.2
Supply Voltage (V)
Start-Up Time
Start-Up Time
(50mA Load)
(100mA Load)
EN_FLSH
(1V/div)
EN_FLSH
(1V/div)
VOUT_FL
(1V/div)
VOUT_FL
(1V/div)
μs/div
100μ
μs/div
100μ
Load Response vs. Time
Load Response vs. Time
(50mA Load)
(100mA Load)
VIN = 3.5V
VIN = 3.5V
VOUT_FL
(10mV/div)
VOUT_FL
(10mV/div)
IOUT
(20mA/div)
IOUT
(50mA/div)
5ms/div
6
3.5
5ms/div
2803.2006.12.1.6
AAT2803
Six-Channel White LED Backlight
Charge Pump with Flash
Typical Characteristics–Flash Driver Charge Pump Section
Output Ripple Voltage vs. Time
Output Ripple Voltage vs. Time
(IOUT = 50mA @ VIN = 3.5V)
(IOUT = 100mA @ VIN = 3.5V)
VIN
(10mV/div)
VIN
(10mV/div)
VOUT
(10mV/div)
VOUT
(20mV/div)
IIN
(10mA/div)
IIN
(10mA/div)
500ns/div
500ns/div
Supply Current vs. Supply Voltage
Oscillator Frequency vs. Supply Voltage
2.75
2.50
Oscillator Frequency (MHz)
Supply Current (mA)
3.00
IOUT = 0μA
C3 = 1μF
VEN_FL = VIN
2.25
2.00
1.75
1.50
1.25
1.00
2.5
3.0
3.5
4.0
Supply Voltage (V)
2803.2006.12.1.6
4.5
5.0
1.30
1.25
+25°C
1.20
1.15
+85°C
-40°C
1.10
2.7
3.2
3.7
4.2
4.7
Supply Voltage (V)
7
AAT2803
Six-Channel White LED Backlight
Charge Pump with Flash
Typical Characteristics–White LED Backlight Driver Section
Unless otherwise noted, VIN = 3.6V, CIN = COUT = C1 = C2 = C3 = 1.0μF; TA = 25°C.
Turn-On to 1X Mode
Efficiency vs. Supply Voltage
(VIN = 4.2V; 20mA Load)
100
4.1mA
VF = 2.9V
10.2mA
VF = 3.1V
20mA
VF = 3.4V
EN
(2V/div)
Efficiency (%)
90
80
CP
(2V/div)
VSINK
(500mV/div)
70
60
IIN
(200mA/div)
50
2.8
3.0
3.2
3.4
3.6
3.8
4.0
4.2
μs/div
100μ
Supply Voltage (V)
Turn-On to 1.5X Mode
Turn-On to 2X Mode
(VIN = 3.8V; 20mA Load)
(VIN = 2.8V; 20mA Load)
EN
(2V/div)
EN
(2V/div)
CP
(2V/div)
VSINK
(500mV/div)
CP
(2V/div)
VSINK
(500mV/div)
IIN
(200mA/div)
IIN
(200mA/div)
μs/div
100μ
μs/div
100μ
Turn-Off from 1.5X Mode
Current Matching vs. Temperature
(VIN = 3.5V; 20mA Load)
20.2
Channel 1
Channel 2
EN
(2V/div)
Current (mA)
20.0
VF
(1V/div)
IIN
(100mA/div)
19.8
Channel 5
19.6
Channel 3
19.4
Channel 4
Channel 6
19.2
-40
μs/div
100μ
8
-20
0
20
40
60
80
Temperature (°°C)
2803.2006.12.1.6
AAT2803
Six-Channel White LED Backlight
Charge Pump with Flash
Typical Characteristics–White LED Backlight Driver Section
Unless otherwise noted, VIN = 3.6V, CIN = COUT = C1 = C2 = C3 = 1.0μF; TA = 25°C.
Load Characteristics
Load Characteristics
(VIN = 3.8V; 1.5X Mode; 15mA Load)
(VIN = 2.9V; 2X Mode; 15mA Load)
VIN
(40mV/div)
VIN
(40mV/div)
CP
(40mV/div)
CP
(40mV/div)
VSINK
(40mV/div)
VSINK
(40mV/div)
500ns/div
500ns/div
Load Characteristics
Load Characteristics
(VIN = 4.0V; 1.5X Mode; 20mA Load)
(VIN = 3.1V; 2X Mode; 20mA Load)
VIN
(40mV/div)
VIN
(40mV/div)
CP
(40mV/div)
CP
(40mV/div)
VSINK
(40mV/div)
VSINK
(40mV/div)
500ns/div
500ns/div
Load Characteristics
Load Characteristics
(VIN = 4.3V; 1.5X Mode; 30mA Load)
(VIN = 3.6V; 2X Mode; 30mA Load)
VIN
(40mV/div)
VIN
(40mV/div)
CP
(40mV/div)
CP
(40mV/div)
VSINK
(40mV/div)
VSINK
(40mV/div)
500ns/div
2803.2006.12.1.6
500ns/div
9
AAT2803
Six-Channel White LED Backlight
Charge Pump with Flash
Typical Characteristics–White LED Backlight Driver Section
Unless otherwise noted, VIN = 3.6V, CIN = COUT = C1 = C2 = C3 = 1.0μF; TA = 25°C.
TLAT vs. VIN
TOFF vs. VIN
350
400
350
300
-40°C
-40°C
300
TOFF (μ
μs)
TLAT (μ
μs)
250
200
150
25°C
85°C
100
250
200
25°C
150
85°C
100
50
50
0
0
2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5
2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5
VIN (V)
VIN (V)
Input Ripple vs. VIN
VIH vs. VIN
1.2
25
1
-40°C
0.9
15
10
VIH (V)
Amplitude (mV)
1.1
30mA
20
20mA
0.7
25°C
0.6
85°C
0.5
10.2mA
5
0.8
0.4
0.3
0.2
0
2.50
2.67
2.84
3.01
3.18
3.35
3.52
3.69
3.86
4.03
4.20
VIN (V)
2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5
VIN (V)
VIL vs. VIN
1.2
1.1
1
VIL (V)
0.9
-40°C
0.8
0.7
0.6
0.5
25°C
85°C
0.4
0.3
0.2
2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5
VIN (V)
10
2803.2006.12.1.6
AAT2803
Six-Channel White LED Backlight
Charge Pump with Flash
Functional Block Diagram
C1+
C1-
Soft-Start
2X
Charge Pump
EN_FL
1MHz
Oscillator
VOUT_FL
VIN
VREF
Soft-Start
Control
1MHz
Oscillator
C2 +
1X
1.5X
2X
Charge
Pump
C2 C3 +
C3 -
Voltage
Reference
6 x 16 bit
ROM
EN/SET
AS 2Cwire
Interface
6 x 16 bit
ROM
VOUT_BL
D/A
D1
D/A
D2
D/A
D3
D/A
D4
D/A
D5
D/A
D6
GND
Functional Description
The AAT2803 is a dual charge pump targeted for
backlight and flash applications. The charge pump
for white LED applications is a tri-mode load switch
(1X) and high efficiency (1.5X or 2X) charge pump
device. To maximize power conversion efficiency,
an internal sensing circuit monitors the voltage
required on each constant current sink input and
sets the load switch and charge pump modes based
on the input battery voltage and the current sink
input voltage. As the battery discharges over time,
the backlight charge pump is enabled when any of
the six current sink inputs near dropout. The charge
pump initially starts in 1.5X mode. If the charge
pump output drops enough for any current source
output to become close to dropout, the charge pump
will automatically transition to 2X mode.
For flash applications, charge pump doubler architecture is used to support the high current demand
required by the application. Charge pump regulation is achieved by sensing the output voltage
2803.2006.12.1.6
through an internal resistor divider network. A
switch doubling circuit is enabled when the divided
output drops below a preset trip point controlled by
an internal comparator. The free-running charge
pump switching frequency is approximately 1MHz.
The charge pump is designed to deliver 120mA of
continuous current and 300mA of pulsed current.
The AAT2803 requires only six external components: three 1μF ceramic capacitors for the charge
pump flying capacitors (C1, C2, and C3), one 1μF
ceramic input capacitor (CIN), one 0.33μF to 1μF
ceramic capacitor for the backlight charge pump
output, and one 1μF for the flash charge pump output. The six constant current sink inputs (D1 to D6)
can drive six individual LEDs with a maximum current of 30mA each. The unused sink inputs must be
connected to VOUT_BL, otherwise the part will operate
only in 2X charge pump mode. The AS2Cwire serial
interface enables the backlight charge pump and
sets the current sink magnitudes. AS2Cwire
addressing allows independent control of two
groups of current sink input: D1 to D4 and D5 to D6.
11
AAT2803
Six-Channel White LED Backlight
Charge Pump with Flash
Constant Current Output Level Settings
AS2Cwire Serial Interface
The constant current sink levels for the white LED
backlight (D1 to D6) are set via the serial interface
according to a logarithmic scale where each code is
1dB lower than the previous code. In this manner,
LED brightness appears linear with each increasing
code count. Because the inputs D1 to D6 are true
independent constant current sinks, the voltage
observed on any single given input will be determined
by the actual forward voltage (VF) for the LED being
driven.
The Advanced Simple Serial Control (AS2Cwire)
single wire interface is used to set the possible
combinations of current levels and LED channel
states. AS2Cwire has addressing capability for
multiple data registers. With multiple data registers, the backlight charge pump main and subchannels can be programmed together or independently from one another.
Since the input current sinks are programmable, no
PWM (pulse width modulation) or additional control
circuitry is needed to control LED brightness. This feature greatly reduces the burden on a microcontroller
or system IC to manage LED or display brightness,
allowing the user to "set it and forget it." With its highspeed serial interface (1MHz data rate), the input sink
current can be changed successively to brighten or
dim LEDs in smooth transitions (e.g., to fade-out) or in
abrupt steps, giving the user complete programmability and real-time control of LED brightness.
The 16 individual current level settings are each
approximately 1dB apart (see Current Level Settings
table). Code 1 is full scale, Code 15 is full scale attenuated by 14dB, and Code 16 is reserved as a "no current" setting.
Data
30mA Max
IOUT (mA)
20mA Max
IOUT (mA)
15mA Max
IOUT (mA)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
30.0
26.7
23.8
21.4
19.0
16.7
15.2
13.3
11.9
10.5
9.5
8.6
7.6
6.7
6.2
0.0
20.0
17.8
15.9
14.3
12.7
11.1
10.2
8.9
7.9
7.0
6.3
5.7
5.1
4.4
4.1
0.0
15.0
13.3
11.9
10.7
9.5
8.3
7.6
6.7
6.0
5.2
4.8
4.3
3.8
3.3
3.1
0.0
AS2Cwire relies on the number of rising edges of
the EN/SET pin to address and load the registers.
AS 2Cwire latches data or address after the
EN/SET pin has been held high for time TLAT.
Address or data is 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 1 is signified by 17 rising
edges, Address 2 by 18 rising edges, and so forth.
Data is set to any number of rising edges between
1 and including 16. A typical write protocol is a
burst of EN/SET rising edges, signifying a particular Address, followed by a pause with EN/SET
held high for the TLAT timeout period, a burst of rising edges signifying Data, and a TLAT timeout for
the data registers. Once an address is set, then
multiple writes to the corresponding data register
are allowed.
When EN/SET is held low for an amount of time
greater than TOFF, the backlight charge pump
enters into shutdown mode and draws less than
1μA from the supply. Address 1 is the default
address on the first rising edge after the backlight
charge pump has been disabled. Whenever shutdown mode is entered, all registers are reset to 1.
Table 1: Current Level Settings.
12
2803.2006.12.1.6
AAT2803
Six-Channel White LED Backlight
Charge Pump with Flash
AS2Cwire Serial Interface Timing
Address
Data
T HI
T LO
TLAT
TLAT
EN/SET
1
Address
2
17
18
1
1
2...
n <= 16
2
Data Reg 1
1
Data Reg 2
1
n
AS2Cwire Addressing
Max Current and Low Current Registers
Five addresses are available to enable all of the
part's functionality. Two 4-bit registers control the
main and sub-channels, giving 16 settings for each.
The main and sub-channels are programmed to the
same constant current level by using Address 1.
Use Addresses 2 and 3 to program the main and
sub-channels independently. Use Address 4 to program the Max Current register, which sets the Max
Current scale. Lastly, Address 5 programs the Low
Current register. The Low Current register controls
the efficient Low Current mode. When the Max
Current register is programmed to 1, 2, or 3, changing the data for Addresses 1-3 will result in the corresponding values found in the Constant Current
Programming Levels table.
Use the Max Current and Low Current registers to
program constant current settings outside of the
20mA Max scale. By default (without changing the
Max Current register), the backlight charge pump
operates in the 20mA Max scale (see Constant
Current Programming Levels). For example, to
change to the 30mA Max scale, address the Max
Current register with 20 rising edges and pause for
TLAT. Program the Max Current register with 2 rising
edges and pause for TLAT. The part will next operate
in the same Data row, but for the setting found in the
30mA Max column. Next, to change to a different
setting on the 30mA Max scale, address the D1-D6
register with 17 rising edges. Program the new constant current level with 1-16 rising edges. The part
will update to the new Data setting according to the
Constant Current Programming Levels table.
When the Max Current register is programmed to 4,
the part is programmed to operate in Low Current
mode and the Data for Addresses 1-3 is irrelevant.
In Low Current mode, the Low Current register
takes precedence. See the Low Current Register
Settings table below for the current level settings
and main/sub-configurations that result.
Address
EN/SET
Edges
Addressed
Register
1
17
2
3
4
5
18
19
20
21
1&2: D1-D6
Current
1: D1-D4 Current
2: D5-D6 Current
3: Max Current
4: Low Current
2803.2006.12.1.6
The backlight charge pump has a distinct Low
Current mode with ultra-low quiescent current. For
drive currents of 2mA or less, the part operates with
significantly reduced quiescent current. This is particularly useful for applications requiring an "always
on" condition such as transmissive displays. As an
example, to change to Low Current mode, address
the Max Current register with 20 rising edges and
pause for TLAT. Program the Max Current register
with 4 rising edges and pause for TLAT. Address the
Low Current register with 21 rising edges and
pause for TLAT. Program the Low Current register
with 1-16 rising edges. The part will update to the
new Low Current mode setting and operate with
significantly reduced quiescent current.
13
AAT2803
Six-Channel White LED Backlight
Charge Pump with Flash
Max Current Register Settings—Address 4
Data
Max Current
1
2
3
4
20mA Max Scale
30mA Max Scale
15mA Max Scale
Low Current Mode
Low Current Register Settings—Address 5
Data
D1-D4 (mA)
D5-D6 (mA)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
0
0
0
0
0
0
0
0
0.05
0.5
1
2
0.05
0.5
1
2
0
0
0
0
0.05
0.5
1
2
0
0
0
0
0.05
0.5
1
2
Disabled Current Sinks
The backlight charge pump is equipped with an autodisable feature to protect against an LED failure condition. Current sink inputs that are not used should
be disabled. To disable and properly terminate
unused current sink inputs, they must be tied to VOUT.
If left unconnected or terminated to ground, the part
will be forced to operate in 2X charge pump mode.
Properly terminating unused current sink inputs is
important to prevent the charge pump modes from
activating prematurely. When properly terminated,
only a small sense current flows for each disabled
channel. The sense current for each disabled channel is less than 120μA.
14
Applications Information
LED Selection
Although the AAT2803 is specifically intended for
driving white LEDs, the device can also be used to
drive most types of LEDs with forward voltage
specifications ranging from 2.0V to 4.7V. LED
applications may include main and sub-LCD display backlighting, camera photo-flash applications,
color (RGB) LEDs, infrared (IR) diodes for remotes,
and other loads benefiting from a controlled output
current generated from a varying input voltage.
In some instances (e.g., in high-luminous-output
applications such as photo flash), it may be necessary to drive high-VF type LEDs. The low-dropout
current sinks in the AAT2803 make it capable of
driving LEDs with forward voltages as high as 4.7V
at full current from an input supply as low as 3.0V.
Outputs can be paralleled to drive high-current
LEDs without complication.
Device Switching Noise Performance
The AAT2803 operates at a fixed frequency of
approximately 1MHz to control noise and limit harmonics that can interfere with the RF operation of
cellular telephone handsets or other communication devices. Back-injected noise appearing on the
input pin of the charge pump is 20mV peak-topeak, typically ten times less than inductor-based
DC/DC boost converter white LED backlight solutions. The AAT2803 soft-start feature prevents
noise transient effects associated with inrush currents during start-up of the charge pump circuit.
Capacitor Selection
Careful selection of the six external capacitors CIN,
C1, C2, C3, and COUT (for backlight and flash) is
important because they will affect turn-on time,
output ripple, and transient performance. Optimum
performance will be obtained when low equivalent
series resistance (ESR) ceramic capacitors are
used. In general, low ESR may be defined as less
than 100mΩ. A value of 1μF for all four capacitors
is a good starting point when choosing capacitors.
If the LED current sources are only programmed
for light current levels, then the capacitor size may
be decreased.
2803.2006.12.1.6
AAT2803
Six-Channel White LED Backlight
Charge Pump with Flash
Capacitor Characteristics
Ceramic Capacitor Materials
Ceramic composition capacitors are highly recommended over all other types of capacitors for use
with the AAT2803. 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
PCB footprint, and is non-polarized. Low ESR
ceramic capacitors help maximize charge pump
transient response. Since ceramic capacitors are
non-polarized, they are not prone to incorrect connection damage.
Ceramic capacitors less than 0.1μF are typically
made from NPO or C0G materials. NPO and C0G
materials typically have tight tolerance and are stable over temperature. Larger capacitor values are
typically composed of X7R, X5R, Z5U, or Y5V
dielectric materials. Large ceramic capacitors, typically greater than 2.2μF, are often available in lowcost Y5V and Z5U dielectrics, but capacitors
greater than 1μF are not typically required.
Equivalent Series Resistance
ESR is an important characteristic to consider when
selecting a capacitor. ESR is a resistance internal
to a capacitor that is caused by the leads, internal
connections, size or area, material composition,
and ambient temperature. Capacitor ESR is typically measured in milliohms for ceramic capacitors
and can range to more than several ohms for tantalum or aluminum electrolytic capacitors.
2803.2006.12.1.6
Capacitor area is another contributor to ESR.
Capacitors that are physically large will have a lower
ESR when compared to an equivalent material
smaller capacitor. These larger devices can improve
circuit transient response when compared to an
equal value capacitor in a smaller package size.
15
AAT2803
Six-Channel White LED Backlight
Charge Pump with Flash
Ordering Information
Package
Marking1
Part Number (Tape and Reel)2
QFN44-24
OFXYY
AAT2803ISK-4.5-T1
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.
Package Information3
QFN44-24
0.4 ± 0.05
24
1
2.7 ± 0.05
0.5 BSC
R0.030Max
13
6
12
4.000 ± 0.050
7
2.7 ± 0.05
Top View
0.025 ± 0.025
Bottom View
0.214 ± 0.036
0.900 ± 0.050
4.000 ± 0.050
19
18
0.300 × 45°
Pin 1 Identification
0.305 ± 0.075
Pin 1 Dot By Marking
Side View
All dimensions in millimeters.
1. XYY = assembly and date code.
2. Sample stock is generally held on part numbers listed in BOLD.
3. The leadless package family, which includes QFN, TQFN, DFN, TDFN and STDFN, has exposed copper (unplated) at the end of the
lead terminals due to the manufacturing process. A solder fillet at the exposed copper edge cannot be guaranteed and is not required
to ensure a proper bottom solder connection.
© 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.
Customers are advised to obtain the latest version of relevant information to verify, before placing orders, that information being relied on is current and complete. All products are sold subject to the terms and conditions of sale supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement, and limitation of liability. AnalogicTech
warrants performance of its semiconductor products to the specifications applicable at the time of sale in accordance with AnalogicTech’s standard warranty. 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.
830 E. Arques Avenue, Sunnyvale, CA 94085
Phone (408) 737- 4600
Fax (408) 737- 4611
16
2803.2006.12.1.6