Analogic AAT2801 Multi-mode charge pump for white led backlight and flash application Datasheet

AAT2801
Multi-Mode Charge Pump for
White LED Backlight and Flash Applications
General Description
Features
The AAT2801 is a member of AnalogicTech's Total
Power Management IC™ (TPMIC™) product family.
It has a dual charge pump architecture designed to
support both the white LED backlight and flash applications for systems operating with Lithium-Ion batteries. The backlight charge pump provides power
required to drive up to four LEDs. To maximize
power efficiency, it automatically selects 1X, 1.5X, or
2X mode. The device produces current levels up to
30mA on each of its four current source outputs.
AnalogicTech's Simple Serial Control™ (S2Cwire™)
interface is used to enable, disable, and set the LED
drive current with a 32-level logarithmic scale LED
brightness control.
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•
VIN Range: 2.7V to 5.5V
Dual Charge Pump
— Flash: Charge Pump Doubler
— Backlight: Tri-Mode Charge Pump
Drives Low-VF and High-VF LEDs
Up to Four 30mA Outputs
32-Position Logarithmic Scale with Digital
Control
Low Noise Constant Frequency Operation
1MHz Switching Frequency
AutoBias Technology
Regulated 4.5/5.0 Volts VOUT_FLASH
Up to 250mA of Current for Flash
Automatic Soft Start
No Inductors
IQ <1µA in Shutdown
Available in 16-pin TDFN44 Package
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•
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•
•
•
•
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•
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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
250mA of pulsed current. It has an independent
enable pin for improved power savings.
ChargePump™
Applications
The AAT2801 is equipped with AnalogicTech’s
AutoBias™ technology which allows individual LEDs
to be powered either by charge pump or battery
input, determined internally and automatically to
maximize the power efficiency even with a large difference in LED forward voltage.
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Display Modules
Mobile Phones
PDAs
Smart Phones
The AAT2801 has thermal protection and built-in
soft-start circuitry. A high charge pump switching frequency enables the use of very small external capacitors. The AAT2801 is available in the 16-pin
TDFN44 package.
Typical Application
C1
1μF
C1 +
C2
1μF
C1- C2+
IN
C3
1μF
C2- C3 +
C3 -
OUT_FLSH
Flash LED
CF
1μF
CP
VIN
CIN
1μF
EN/SET
C CP
1μF
RB
AAT2801
D1
D2
D3
D4
EN/SET
Backlight
D4
Flash Enable
2801.2006.04.1.3
EN_FLSH
D3
D2
D1
GND
1
AAT2801
Multi-Mode Charge Pump for
White LED Backlight and Flash Applications
Pin Descriptions
Pin #
Symbol
1
2
3
4
5
6
7
C3C3+
OUT_FLASH
IN
C1+
C1CP
8
9
10
11
C2+
C2GND
EN/SET
12
13
14
15
D3
D1
D4
D2
16
EN_FLSH
EP
Function
Flying capacitor 3 negative terminal. Connect a 1µF capacitor between C3- and C3+.
Flying capacitor 3 positive terminal.
Flash output voltage. Requires 1µF capacitor connected between this pin and ground.
Input power supply. Requires 1µF capacitor connected between this pin and ground.
Flying capacitor 1 positive terminal. Connect a 1µF capacitor between C1+ and C1-.
Flying capacitor 1 negative terminal.
White LED charge pump output. Requires 1µF capacitor connected between this pin
and ground.
Flying capacitor 2 positive terminal. Connect a 1µF capacitor between C2+ and C3-.
Flying capacitor 2 negative terminal.
Ground.
S2Cwire serial interface control pin for the white LED charge pump. This pin should not
be left floating.
Current source output #3.
Current source output #1.
Current source output #4.
Current source output #2.
Active high enable pin for the flash charge pump. When connected low, the charge
pump shuts down and consumes less than 1µA of current.
Exposed paddle (bottom); connect to GND directly beneath package.
Pin Configuration
TDFN44-16
(Top View)
C3C3+
OUT_FLASH
IN
C1+
C1CP
C2+
2
1
16
2
15
3
14
4
13
5
12
6
11
7
10
8
9
EN_FLSH
D2
D4
D1
D3
EN/SET
GND
C2-
2801.2006.04.1.3
AAT2801
Multi-Mode Charge Pump for
White LED Backlight and Flash Applications
Absolute Maximum Ratings1
Symbol
VIN
VEN/SET
IOUT 2
TJ
Description
Input Voltage
EN/SET to GND Voltage
Maximum DC Output Current
Operating Junction Temperature Range
Value
Units
-0.3 to 6.0
-0.3 to VIN+0.3
120
-40 to 150
V
V
mA
°C
Value
Units
2.0
50
mW
°C/W
Thermal Information
Symbol
PD
θJA
Description
Maximum Power Dissipation
Thermal Resistance3
3, 4
1. Stresses above those listed in Absolute Maximum Ratings may cause permanent damage to the device. Functional operation at conditions other than the operating conditions specified is not implied. Only one Absolute Maximum Rating should be applied at any one time.
2. Based on long-term current density limitation.
3. Mounted on an FR4 board.
4. Derate 6.25mW/°C above 25°C.
2801.2006.04.1.3
3
AAT2801
Multi-Mode Charge Pump for
White LED Backlight and Flash Applications
Electrical Characteristics1
CIN = CCP = CF = C1 = C2 = C3 = 1.0µF; TA = -40°C to 85°C, unless otherwise noted.
Symbol
Description
Input Power Supply
VIN
Operation Range
ICC
ISHDN
IDX
I(D-Match)
Operating Current
Shutdown Current
Output Current Accuracy2
Current Matching3
Flash Charge Pump Output
Voltage
Maximum Continuous IOUT
IOUT
Maximum Pulsed IOUT
ηCP
White LED Charge Pump
Section Efficiency
Charge Pump Section
VOUT
TSS
FCLK
EN/SET
VEN(L)
VEN(H)
TEN/SET LO
TEN/SET HI MIN
TEN/SET HI MAX
TOFF
TLAT
IEN/SET/EN_FLSH
Soft-Start Time
Conditions
Min Typ Max Units
2.7
3.0 ≤ VIN ≤ 5.5, No Load Current; VOUT_FLSH
= 5V, EN/SET = GND, EN_FLSH = VIN
3.0 ≤ VIN ≤ 5.5, EN/SET = VIN, EN_FLSH =
GND, VD1:VD4 = 2.0V, CP = 1X
3.0 ≤ VIN ≤ 5.5, No Load Current; EN/SET =
VIN, EN_FLSH = GND, CP = 1.5X
EN_FLSH = EN/SET = 0
VIN = 3.5, Code = 32, TA = 25°C
-10
VD1:D4 = 3.6, VIN = 3.5V; LED Charge
-3.0
Pump Only
3.0V < VIN < 5V, IOUT = 120mA;
4.3
EN_FLSH = VIN
VIN = 3.6V; VOUT = 4.5V; EN_FLSH = VIN
120
VIN = 3.6V; VOUT = 4.5V; IPulsed < 500mS
250
VIN = 3.5V, IOUT(TOTAL) = 120mA,
Measured from IN to CP
Backlight Charge Pump
Flash Charge Pump
VEN/SET < 0.6V
VEN/SET > 1.4V
VEN/SET > 1.4V
VEN/SET < 0.6V
VEN/SET > 1.4V
VEN/SET/EN_FLSH = 5V, VIN = 5V
5.5
4.5
0.55
3.0
5.0
±0.5
1.0
10
3.0
µA
%
%
4.5
4.7
V
-
mA
93
1.4
0.3
%
µs
MHz
0.4
75
50
-1.0
V
mA
50
200
1.0
Clock Frequency
Enable Threshold Low
Enable Threshold High
EN/SET Low Time
Minimum EN/SET High Time
Maximum EN/SET High Time
EN/SET Off Timeout
EN/SET Latch Timeout
Input Leakage
3.0
75
500
500
1.0
V
V
µs
µs
µs
µs
µs
µA
1. The AAT2801 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. Codes 2 through 7 are guaranteed to be within ±15% of stated current level.
3. Current matching is defined as I(D-Match) = (ID - IAVE)/IAVE.
4
2801.2006.04.1.3
AAT2801
Multi-Mode Charge Pump for
White LED Backlight and Flash Applications
Typical Characteristics–White LED Backlight Driver Section
VIN = 3.5V, CIN = 2.2µF, CCP = C1 = C2 = 1.0µF; TA = 25°C, unless otherwise noted.
Efficiency vs. VIN
Efficiency vs. VIN
(Code 26)
(D1 = 3.5V; D2 = 3.3V; D3 = 3.2V; D4 = 3.0V)
100
100
90
3.0VF
80
Efficiency (%)
Efficiency (%)
90
70
60
50
3.5VF
70
60
50
30
2.9
3.0
3.1
3.2
3.3
3.4
3.5
3.6
3.7
3.8
3.9
4.0
4.1
4.2
Code 32
Code 28
40
40
30
Code 26
80
2.9
3.0
3.1
3.2
3.3
3.5
3.6
3.7
3.8
3.9
4.0
4.1
4.2
Input Voltage (V)
Input Voltage (V)
Efficiency vs. VIN
Operating Current
(D1-D2 = 3.5V; D3-D4 = 3.2V)
(Code 23; EN_FLSH Off)
100
5.0
90
Code 26
V_DX = 3.3V
4.0
80
70
IIN (A)
Efficiency (%)
3.4
60
3.0
2.0
50
30
2.9
3.0
3.1
1.0
Code 32
Code 28
40
3.2
3.3
3.4
3.5
V_DX = 3.0V
3.6
3.7
3.8
3.9
4.0
4.1
4.2
Input Voltage (V)
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
Input Voltage (V)
Operating Current
(Code 23; EN_FLSH On; IOUT = 100mA)
8.0
V_DX = 3.3V
7.0
IIN (A)
6.0
5.0
4.0
3.0
2.0
1.0
V_DX = 3.0V
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
Input Voltage (V)
2801.2006.04.1.3
5
AAT2801
Multi-Mode Charge Pump for
White LED Backlight and Flash Applications
Typical Characteristics–White LED Backlight Driver Section
VIN = 3.5V, CIN = 2.2µF, CCP = C1 = C2 = 1.0µF; TA = 25°C, unless otherwise noted.
Turn-On to 1X Mode
Turn-On to 1X Mode
(4x19mA Load)
(4x30mA Load)
EN/SET
(2V/div)
EN/SET
(2V/div)
VCP
(4V/div)
VCP
(4V/div)
VDIODE
(2V/div)
VDIODE
(2V/div)
IIN
(100mA/div)
IIN
(100mA/div)
Time (100µs/div)
Turn-On to 1.5X Mode
Time (100µs/div)
Turn-Off from Full-Scale 2X Mode
(4x19mA Load)
EN/SET
(2V/div)
EN/SET
(2V/div)
VCP
(4V/div)
VDIODE
(2V/div)
VDIODE
(2V/div)
IIN
(200mA/div)
IIN
(100mA/div)
Time (100µs/div)
Time (100µs/div)
Flash Section Turn-On
Flash Section Turn-On
(VIN = 3.5V; IOUT = 100mA; EN/SET = GND)
(VIN = 3.5V; IOUT = 200mA; EN/SET = GND)
EN_FLSH
(2V/div)
EN_FLSH
(2V/div)
VOUT
(2V/div)
VOUT
(2V/div)
IIN
(100mA/div)
IIN
(100mA/div)
Time (100µs/div)
6
Time (100µs/div)
2801.2006.04.1.3
AAT2801
Multi-Mode Charge Pump for
White LED Backlight and Flash Applications
Typical Characteristics–White LED Backlight Driver Section
VIN = 3.5V, CIN = 2.2µF, CCP = C1 = C2 = 1.0µF; TA = 25°C, unless otherwise noted.
Charge Pump to Load Switch
Charge Pump to Load Switch
(1.5X Mode; 4x19mA Load)
(1.5X Mode; 4x30mA Load)
VIN
(500mV/div)
VIN
(500mV/div)
VCP
(1V/div)
VDIODE
(500mV/div)
VCP
(1V/div)
VDIODE
(500mV/div)
IIN
(50mA/div)
IIN
(50mA/div)
Time (5ms/div)
Time (5ms/div)
Charge Pump to Load Switch
Charge Pump to Load Switch
(2X Mode; 4x19mA Load)
(2X Mode; 4x30mA Load)
VIN
(500mV/div)
VIN
(500mV/div)
VCP
(1V/div)
VCP
(1V/div)
VDIODE
(500mV/div)
VDIODE
(500mV/div)
IIN
(50mA/div)
IIN
(50mA/div)
Time (5ms/div)
Time (5ms/div)
Load Switch to Charge Pump
Load Switch to Charge Pump
(1.5X Mode; 4x19mA Load)
(1.5X Mode; 4x30mA Load)
VIN
(1V/div)
VIN
(1V/div)
VCP
(4V/div)
VCP
(4V/div)
VDIODE
(500mV/div)
VDIODE
(500mV/div)
IIN
(50mA/div)
IIN
(50mA/div)
Time (2ms/div)
2801.2006.04.1.3
Time (2ms/div)
7
AAT2801
Multi-Mode Charge Pump for
White LED Backlight and Flash Applications
Typical Characteristics–White LED Backlight Driver Section
VIN = 3.5V, CIN = 2.2µF, CCP = C1 = C2 = 1.0µF; TA = 25°C, unless otherwise noted.
Line Response
Line Response
(1X Mode; 4x19mA Load)
(1X Mode; 4x30mA Load)
VIN
(0.5V/div)
VIN
(0.5V/div)
VLED
(20mV/div)
VLED
(20mV/div)
VCP
(0.5V/div)
VCP
(0.5V/div)
ID
(10mA/div)
ID
(10mA/div)
Time (1ms/div)
Time (1ms/div)
Line Response
Line Response
(1.5X Mode; 4x19mA Load)
(1.5X Mode; 4x30mA Load)
VIN
(0.5V/div)
VIN
(0.5V/div)
VDX
(20mV/div)
VLED
(20mV/div)
VCP
(0.5V/div)
VCP
(0.5V/div)
IDX
(10mA/div)
ID
(10mA/div)
Time (1ms/div)
Time (1ms/div)
Line Response
(IOUT = 100mA; I_DX = 4x19mA; 1.5X Mode)
VIN
(0.5V/div)
VCP
(0.5V/div)
VDX
(20mV/div)
IDX
(10mA/div)
VF
(10mV/div)
Time (1ms/div)
8
2801.2006.04.1.3
AAT2801
Multi-Mode Charge Pump for
White LED Backlight and Flash Applications
Typical Characteristics–White LED Backlight Driver Section
VIN = 3.5V, CIN = 2.2µF, CCP = C1 = C2 = 1.0µF; TA = 25°C, unless otherwise noted.
Operating Characteristics
Operating Characteristics
(I_DX = 4x15mA; 1.5X Mode)
(I_DX = 4x15mA; 1.5X Mode; IOUT = 100mA)
VIN = 3.0V
VDX
(20mV/div)
VIN = 3.0V
VDX
(20mV/div)
IIN
(10mA/div)
IIN
(10mA/div)
VCP
(20mV/div)
VCP
(20mV/div)
VF
(40mV/div)
Time (1µs/div)
Time (1µs/div)
Operating Characteristics
Operating Characteristics
(I_DX = 4x30mA; 1.5X Mode)
(I_DX = 4x30mA; 1.5X Mode; IOUT = 100mA)
VIN = 3.5V
VDX
(20mV/div)
VDX
(20mV/div)
IIN
(10mA/div)
IIN
(10mA/div)
VCP
(40mV/div)
VCP
(40mV/div)
VF
(40mV/div)
Time (1µs/div)
Time (1µs/div)
Input Current vs. Input Voltage
Input Current vs. Input Voltage
(4x10mA)
(4x30mA)
90
300
80
VDIODE = 3.4V
70
250
VDIODE = 3.4V
200
IIN (mA)
IIN (mA)
60
50
40
30
20
VDIODE = 3.0V
10
3.1
3.5
3.9
4.3
Input Voltage (V)
2801.2006.04.1.3
100
50
0
2.7
150
4.7
5.1
5.5
0
2.7
VDIODE = 3.0V
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Input Voltage (V)
9
AAT2801
Multi-Mode Charge Pump for
White LED Backlight and Flash Applications
Typical Characteristics–White LED Backlight Driver Section
VIN = 3.5V, CIN = 2.2µF, CCP = C1 = C2 = 1.0µF; TA = 25°C, unless otherwise noted.
Diode Current vs. Input Voltage
VIH and VIL vs. VIN
(30mA; 15mA settings)
0.850
40
0.825
IDIODE (mA)
35
0.800
VDIODE = 3.4V
0.775
30
0.725
VIL
0.700
20
0.675
VDIODE = 3.4V
15
0.650
0.625
0.600
10
2.7
3.1
3.5
3.9
4.3
Input Voltage (V)
10
VIH
0.750
25
4.7
5.1
5.5
2.5
3.0
3.5
4.0
4.5
5.0
5.5
Input Voltage (V)
2801.2006.04.1.3
AAT2801
Multi-Mode Charge Pump for
White LED Backlight and Flash Applications
Typical Characteristics–Flash Driver Charge Pump Section
VIN = 3.5V, CIN = 2.2µF, C3 = CF = 1.0µF, TA = 25°C, unless otherwise noted.
Output Voltage vs. Output Current
Efficiency vs. Supply Voltage
5.0
100
VIN=3.3
4.6
VIN=3.6
50mA
90
80
4.4
4.2
4.0
3.8
VIN = 3.0
VIN = 2.7
3.6
3.4
Efficiency (%)
Output Voltage (V)
4.8
3.2
70
60
100mA
50
150mA
40
30
20
10
3.0
0
40
80
120
160
0
200
2.7
3.0
Output Current (mA)
Efficiency vs. Load Current
Maximum Current Pulse (mA)
VIN = 3.0V
VIN = 2.7V
Efficiency (%)
80
70
60
50
VIN = 3.6V
40
VIN = 3.3V
30
20
10
0
0.1
1.0
10
100
3.9
4.2
4.5
1000
600
500
400
300
One-shot pulse duration = 250ms
VOUT> 4.0V
200
100
0
3.0
3.2
3.4
3.6
3.8
4.0
4.2
Supply Voltage (V)
Load Current (mA)
Load Response
Load Response
(100mA Load)
(50mA Load)
VIN = 3.5V
VIN = 3.5V
VOUT
(10mV/div)
VOUT
(10mV/div)
IOUT
(50mA/div)
IOUT
(20mA/div)
Time (5ms/div)
2801.2006.04.1.3
3.6
Maximum Current Pulse vs. Supply Voltage
100
90
3.3
Supply Voltage (V)
Time (5ms/div)
11
AAT2801
Multi-Mode Charge Pump for
White LED Backlight and Flash Applications
Typical Characteristics–Flash Driver Charge Pump Section
VIN = 3.5V, CIN = 2.2µF, C3 = CF = 1.0µF, TA = 25°C, unless otherwise noted.
Startup
VEN Threshold vs. Supply Voltage
1.00
VEN Threshold (V)
0.95
ENABLE
(1V/div)
ILOAD = 150mA @ VIN = 3.3V
ILOAD = 100mA @ VIN = 3.0V
ILOAD = 150mA @ VIN = 3.3V
VOUT
(1V/div)
0.90
VIH
0.85
0.80
0.75
VIL
0.70
0.65
0.60
0.55
0.50
2.7
3.1
3.5
3.9
4.3
4.7
5.1
5.5
Supply Voltage (V)
Time (100µs/div)
Normalized Output Voltage (%)
Normalized Output Voltage vs. Temperature
2.0
IOUT = 25mA
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
-50
-30
-10
10
30
50
70
90
Temperature (°C)
12
2801.2006.04.1.3
AAT2801
Multi-Mode Charge Pump for
White LED Backlight and Flash Applications
Functional Block Diagram
C3 +
C3 -
OUT_FLSH
2X CP
Soft Start
EN_FLSH
1MHz
Oscillator
IN
VREF
Soft-Start
Control
1MHz
Oscillator
Voltage
Reference
EN/SET
Control
Logic
C1+
1X
1.5X
2X
Charge
Pump
C1C2+
C2CP
D/A
D1
D/A
D2
D/A
D3
D/A
D4
GND
Functional Description
The AAT2801 is a dual charge pump for white
LED and flash applications. The charge pump for
white LED application is a tri-mode load switch
(1X) and high efficiency (1.5X or 2X) charge
pump device intended for white LED backlight
applications. To maximize power conversion efficiency, an internal sensing circuit monitors the
voltage required on each constant current source
output and sets the load switch and charge pump
modes based on the input battery voltage and the
current source output voltage. As the battery discharges over time, the AAT2801 charge pump is
enabled when any of the four current source outputs nears dropout. The charge pump initially
2801.2006.04.1.3
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.
The second section of the AAT2801 contains a
voltage doubling charge pump to supply flash LED
functions. The voltage doubling charge pump provides a 4.5V regulated output and has an independent enable control.
AutoBias Technology
Each of the four current source outputs for the
white LED backlight charge pump section is independently switched between the battery input (1X)
or the charge pump output (1.5X or 2X), depending
13
AAT2801
Multi-Mode Charge Pump for
White LED Backlight and Flash Applications
Applications Information—
White LED Backlight Section
on the voltage at the current source output. Since
the LED to LED VF can vary as much as 1 volt, this
function significantly enhances overall efficiency of
the white LED backlight charge pump section when
the battery input voltage level is greater than the
voltage required at any current source output.
Constant Current Output Level Settings
The constant current source amplitudes for D1 to D4
are set via the serial interface according to a logarithmic scale, where each code is 1dB greater than
the previous code. In this manner, LED brightness
appears linear with each increasing code count.
Because the outputs D1 to D4 are true independent
constant current sources, the voltage observed on
any single given output will be determined by the
actual forward voltage (VF) for the LED being driven.
Flash Driver
For flash applications, the voltage doubling
charge pump section is used to support the high
current demand required by the application.
Charge pump regulation is achieved by sensing
the output voltage through an internal resistor
divider network. The free running charge pump
switching frequency is approximately 1MHz. The
charge pump is designed to deliver up to 120mA
of continuous current and 250mA of pulsed current for up to 500ms.
Since the output current of the AAT2801 is 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 high-speed serial interface (1MHz
data rate), the output current of the AAT2801 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 AAT2801 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 1µF
ceramic charge pump output capacitor (CCP), and
one 1µF for the flash output (CF). The four constant current outputs (D1 to D4) drive four individual LEDs with a maximum current of 30mA each.
The EN/SET S2Cwire serial interface enables the
AAT2801 and sets the current source magnitudes. A separate flash enable pin (EN_FLSH) is
provided to independently control the flash charge
pump circuit.
The 32 individual current level settings are each
approximately 1dB apart (see Current Level
Settings below). Code 32 is full scale; Code 2 is full
scale attenuated by 31dB; and Code 1 is reserved
as a "no current" setting.
Normalized Current Level Settings
Current (mA)
1.00
0.10
0.01
0.00
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
Code
14
2801.2006.04.1.3
AAT2801
Multi-Mode Charge Pump for
White LED Backlight and Flash Applications
Constant Current Source Output
Nominal Programming Levels (mA)
S2Cwire Serial Interface
Code
IOUT (typ)
(mA)
Code
IOUT (typ)
(mA)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
0.0
0.1
0.2
0.4
0.5
0.7
1.1
1.8
2.0
2.2
2.5
2.8
3.2
3.5
4.0
4.5
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
5.1
5.6
6.4
7.2
8.1
9.2
10.2
11.5
13.1
14.7
16.6
18.6
20.9
23.6
26.6
30.0
The current source output magnitude is controlled
by the EN/SET pin, using AnalogicTech's S2Cwire
interface. The interface records rising edges of
the EN/SET pin and decodes them into 32 individual current level settings each 1dB apart with
Code 1 reserved for no current. Once EN/SET
has been held in the logic high state for time TLAT,
the programmed current is seen at the current
source outputs, and the internal data register is
reset to 0. For subsequent current level programming, the number of rising edges corresponding to the desired code must be entered on the
EN/SET pin.
When EN/SET is held low for an amount of time
greater than TOFF, the AAT2801 enters into shutdown mode and draws less than 1µA from VIN.
The internal data register is reset to 0 during shutdown.
S2Cwire Serial Interface Timing Diagram
THI
TLO
TOFF
TLAT
EN/SET
1
Data Reg
2
n-1
n <= 32
0
Termination of Unused Current Source
Outputs
If any outputs (D1 to D4) are not used, they should
be terminated by connecting the respective unused
output directly to ground. This is required to assure
correct charge pump mode operation. If a given
unused output is not terminated to ground, it will
appear to the respective output’s feedback control
as an infinite impedance load and the unused constant current source will be set to maximum voltage. Although no current flows from the unused
current source, the voltage sensed at that node
could force the charge pump control to activate the
2801.2006.04.1.3
n
0
charge pump when it is not necessary. To prevent
this effect, simply connect unused constant current
source outputs to ground.
LED Selection
The AAT2801 is specifically intended for driving
white LEDs. However, the device design will allow
the AAT2801 to drive most types of LEDs with forward voltage specifications ranging from 2.0V to
4.3V. Since the D1 to D4 output current sources
are matched with negligible voltage dependence,
the LED brightness will be matched regardless of
the specific LED forward voltage (VF) levels.
15
AAT2801
Multi-Mode Charge Pump for
White LED Backlight and Flash Applications
Applications Information—
White LED Charge Pump Section
Power Efficiency and Device
Evaluation
The charge pump efficiency discussion in the following sections only accounts for efficiency of the
charge pump section itself. Due to the unique circuit
architecture and design of the AAT2801, it is very
difficult to measure efficiency in terms of a percent
value comparing input power over output power.
Since the AAT2801 outputs are pure constant current sources and typically drive individual loads, it
is difficult to measure the output voltage for a given
output (D1 to D4) to derive an overall output power
measurement. For any given application, white
LED forward voltage levels can differ, yet the output drive current will be maintained as a constant.
This makes quantifying output power a difficult task
when taken in the context of comparing to other white
LED driver circuit topologies. A better way to quantify
total device efficiency is to observe the total input
power to the device for a given LED current drive
level. The best white LED driver for a given application should be based on trade-offs of size, external
components count, reliability, operating range, and
total energy usage...not just "% efficiency."
Efficiency of the AAT2801 can be quantified under
very specific conditions and is dependent upon the
input voltage versus the output voltage seen across
the loads applied to outputs D1 through D4 for a
given constant current setting. Depending upon the
case of VIN being greater than the specific voltage
seen across the load on D1 to D4, the device will
operate in load switch mode. If the voltage seen on
any constant current source output is less than VIN,
then the device will operate in 1.5X or 2X charge
pump mode. Each of these modes will yield different efficiency values. One should refer to the following two sections for explanations for each operational mode.
Load Switch Mode Efficiency
The AAT2801 load switch mode is operational at all
times and functions alone to enhance device power
conversion efficiency when the condition exists
where VIN is greater than voltage across the load
connected to the constant current source outputs.
When in load switch mode, the voltage conversion
efficiency is defined as output power divided by
input power:
η=
The expression to define the ideal efficiency (η)
can be rewritten as:
η=
POUT VOUT × IOUT VOUT
=
=
PIN
VIN × IOUT
VIN
-or-
η(%) = 100
⎛ VOUT ⎞
⎝ VIN ⎠
Charge Pump Section Efficiency
The AAT2801 contains a dual mode fractional and
voltage doubling charge pump which will boost the
input supply voltage in the event where VIN is less
than the voltage required on the constant current
source outputs. The efficiency (η) can be simply
defined as a linear voltage regulator with an effective output voltage that is equal to one and one half
or two times the input voltage. Efficiency (η) for an
ideal 1.5X charge pump can typically be expressed
as the output power divided by the input power.
η=
16
POUT
PIN
POUT
PIN
2801.2006.04.1.3
AAT2801
Multi-Mode Charge Pump for
White LED Backlight and Flash Applications
In addition, with an ideal 1.5X charge pump, the
output current may be expressed as 2/3 of the
input current. The expression to define the ideal
efficiency (η) can be rewritten as:
VOUT × IOUT
VOUT
POUT
=
=
PIN
VIN × 1.5IOUT 1.5VIN
η=
-or-
η(%) = 100
⎛ VOUT ⎞
⎝ 1.5VIN⎠
For the voltage doubling charge pump mode, the
expression to define the ideal efficiency (η) can be
rewritten as:
η=
V
POUT VOUT × IOUT
=
= OUT
PIN
VIN × 2IOUT
2VIN
-or⎛ VOUT ⎞
η(%) = 100
⎝ 2VIN ⎠
The flash driver charge pump section utilizes a 2X
voltage doubling topology; thus, the same efficiency equation may be used to calculate the flash
charge pump efficiency.
Capacitor Selection
Careful selection of the six external capacitors CIN,
C1, C2, C3, CCP, and CF 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 six capacitors is a good starting
point when choosing capacitors. If the LED current
sources are only programmed for light current lev-
2801.2006.04.1.3
els, then the capacitor size may be decreased.
Conversely, if the flash driver charge pump is to
provide the maximum flash current of 250mA, CIN
may be increased to 2.2µF or more to reduce the
load transient effects of the flash driver output.
Capacitor Characteristics
Ceramic composition capacitors are highly recommended over all other types of capacitors for use
with the AAT2801. 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.
Thermal Protection
The AAT2801 has a thermal protection circuit that
will shut down the charge pump if the die temperature rises above the thermal limit.
Flash LED Driver
The AAT2801 flash driver charge pump circuit can
source 250mA for pulsed loads up to 500ms from
an input supply as low as 3.3V. This makes the
device well suited for low-cost flash LED driver
applications in portable products. Typically the
4.5V flash output (OUT_FLSH) version of the
AAT2801 should be selected for photo flash LED
applications, as it can maintain better voltage regulation at higher pulsed load current levels (refer to
Figure 1). The limitation of this option is that the
greatest flash LED forward voltage (VF) that can be
driven is 4.5V at the maximum set forward current
(IF) for the application. Flash LEDs with forward
voltage (VF) levels up to 5.0V can be driven by the
AAT2801 5.0V output option. However, the maximum current for a 500ms pulse will be reduced.
Refer to the Typical Characteristics flash driver
curves for peak output current levels for a given
minimum input voltage.
17
AAT2801
Multi-Mode Charge Pump for
White LED Backlight and Flash Applications
C3
1μF
C3+
VIN
IN
C3-
4.5V
OUT_FLSH
CIN
1μF
CF
1μF
Flash LED
AAT2801
RB
Flash Enable
EN_FLSH
Figure 1: Flash LED Application.
The forward current (IF) through the flash LED may
be determined with the use of a series ballast resistor. The typical forward voltage (VF) for the flash
LED in a given application should be derived from
the LED manufacturer's datasheet for the desired
forward current (IF) of the flash application. Once
the forward current has been determined, the flash
ballast resistor can be calculated using the following equation:
RB =
RL =
(VOUT - VF)
IF
Where:
=
Flash ballast resistor value in ohms (Ω)
VOUT =
Regulated charge pump output voltage
(typically 4.5V)
VF
=
Flash LED forward voltage at the
desired forward current
IF
=
Desired flash LED forward current
The flash LED function can be controlled by the
AAT2801 flash enable (EN_FLSH) pin in most
18
If a "light" or "movie" mode is also needed along
with the flash function, this can be accomplished
with the addition of a second ballast resistor with a
flash function gating MOSFET switch as shown in
Figure 2. Refer to the following equations for the
calculation of flash and light resistors, RB and RL.
(VOUT - VF)
IF
Where:
RB
applications. The device start-up time into a maximum load is about 200µs, thus eliminating the
need for pre-flash control synchronization.
RL
=
Light mode ballast resistor value in
ohms (Ω)
VOUT =
Regulated charge pump output voltage
(typically 4.5V)
VF
=
Flash LED forward voltage at the
desired forward current
IF
=
Desired flash LED forward current in
the "light" mode
2801.2006.04.1.3
AAT2801
Multi-Mode Charge Pump for
White LED Backlight and Flash Applications
C3
1μF
C3+
VIN
IN
C3-
4.5V
OUT_FLSH
CIN
1μF
COUT
1μF
Flash LED
AAT2801
Flash Enable
EN_FLSH
RL
RB
Flash Enable
Figure 2: Flash LED Driver with Gated Flash Application.
RB =
(VOUT - VF)
- RDS
IF
Where:
RB
=
Flash ballast resistor value in ohms (Ω)
RDS
=
Flash gating mosfet on resistance
VOUT =
Regulated charge pump output voltage
(typically 4.5V)
VF
=
Flash LED forward voltage at the
desired forward current
IF
=
Desired flash LED forward current
2801.2006.04.1.3
19
AAT2801
Multi-Mode Charge Pump for
White LED Backlight and Flash Applications
Ordering Information
Output Voltage
Package
Marking1
Part Number (Tape and Reel)2
4.5V
5.0V
TDFN44-16
TDFN44-16
MSXYY
AAT2801IXN-4.5-T1
AAT2801IXN-5.0-T1
Package Information
3.30 ± 0.05
Detail "B"
4.00 ± 0.05
Index Area
(D/2 x E/2)
0.3 ± 0.10
0.375 ± 0.125
0.16
0.075 ± 0.075
0.1 REF
4.00 ± 0.05
2.60 ± 0.05
Top View
Pin 1 Indicator
(optional)
0.23 ± 0.05
Bottom View
0.45 ± 0.05
Detail "A"
0.229 ± 0.051
+ 0.05
0.8 -0.20
7.5° ± 7.5°
0.05 ± 0.05
Detail "B"
Option A:
C0.30 (4x) max
Chamfered corner
Side View
Option B:
R0.30 (4x) max
Round corner
Detail "A"
All dimensions in millimeters.
1. XYY = assembly and date code.
2. Sample stock is generally held on part numbers listed in BOLD.
© 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
20
2801.2006.04.1.3