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Multi-Mode Charge Pump for White LED Backlight and Flash Applications General Description
The AAT2801 is a member of AnalogicTech's Total Power Management ICTM (TPMICTM) 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 ControlTM (S2CwireTM) interface is used to enable, disable, and set the LED drive current with a 32-level logarithmic scale LED brightness control. 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. The AAT2801 is equipped with AnalogicTech's AutoBiasTM 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. 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.
AAT2801
Features
* * * * * * * * * * * * * *
ChargePumpTM
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 <1A in Shutdown Available in 16-pin TDFN44 Package
Applications
* * * * Display Modules Mobile Phones PDAs Smart Phones
Typical Application
C1 1F C2 1F C3 1F C1 + IN C1- C2+ C2- C3 + C3 CF 1F CP VIN CIN 1F C CP 1F RB
OUT_FLSH
Flash LED
AAT2801
D1 D2 D3 D4 D4 D3 D2
Backlight
D1
EN/SET Flash Enable
EN/SET EN_FLSH
GND
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Multi-Mode Charge Pump for White LED Backlight and Flash Applications Pin Descriptions
Pin #
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 EP
AAT2801
Symbol
C3C3+ OUT_FLASH IN C1+ C1CP C2+ C2GND EN/SET D3 D1 D4 D2 EN_FLSH
Function
Flying capacitor 3 negative terminal. Connect a 1F capacitor between C3- and C3+. Flying capacitor 3 positive terminal. Flash output voltage. Requires 1F capacitor connected between this pin and ground. Input power supply. Requires 1F capacitor connected between this pin and ground. Flying capacitor 1 positive terminal. Connect a 1F capacitor between C1+ and C1-. Flying capacitor 1 negative terminal. White LED charge pump output. Requires 1F capacitor connected between this pin and ground. Flying capacitor 2 positive terminal. Connect a 1F 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 1A of current. Exposed paddle (bottom); connect to GND directly beneath package.
Pin Configuration
TDFN44-16 (Top View)
C3C3+ OUT_FLASH IN C1+ C1CP C2+
1 2 3 4 5 6 7 8
16 15 14 13 12 11 10 9
EN_FLSH D2 D4 D1 D3 EN/SET GND C2-
2
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Multi-Mode Charge Pump for White LED Backlight and Flash Applications Absolute Maximum Ratings1
Symbol
VIN VEN/SET IOUT 2 TJ
AAT2801
Description
Input Voltage EN/SET to GND Voltage Maximum DC Output Current Operating Junction Temperature Range
Value
-0.3 to 6.0 -0.3 to VIN+0.3 120 -40 to 150
Units
V V mA C
Thermal Information
Symbol
PD JA
Description
Maximum Power Dissipation Thermal Resistance3
3, 4
Value
2.0 50
Units
mW C/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 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 25C. 2801.2006.04.1.3
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Multi-Mode Charge Pump for White LED Backlight and Flash Applications Electrical Characteristics1
CIN = CCP = CF = C1 = C2 = C3 = 1.0F; TA = -40C to 85C, unless otherwise noted. Symbol Description Conditions Min Typ Max Units
5.5 4.5 V
AAT2801
Input Power Supply VIN Operation Range
ICC
Operating Current
ISHDN IDX I(D-Match) VOUT
Shutdown Current Output Current Accuracy2 Current Matching3
Flash Charge Pump Output Voltage Maximum Continuous IOUT IOUT Maximum Pulsed IOUT CP White LED Charge Pump Section Efficiency Charge Pump Section 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 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
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 = 25C -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
3.0 0.55 3.0
mA 5.0 1.0 10 3.0 4.7 A % % V mA %
0.5 4.5
93
50 200 1.0 1.4 0.3 50 -1.0 75 500 500 1.0 0.4 75
s MHz V V s s s s s A
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
1. The AAT2801 is guaranteed to meet performance specifications over the -40C to 85C 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
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Multi-Mode Charge Pump for White LED Backlight and Flash Applications Typical Characteristics-White LED Backlight Driver Section
VIN = 3.5V, CIN = 2.2F, CCP = C1 = C2 = 1.0F; TA = 25C, unless otherwise noted.
AAT2801
Efficiency vs. VIN
(Code 26)
100 90 100 90
Efficiency vs. VIN
(D1 = 3.5V; D2 = 3.3V; D3 = 3.2V; D4 = 3.0V)
Efficiency (%)
Efficiency (%)
80 70 60 50 40 30 2.9 3.0 3.1
3.0VF
80 70 60 50 40 30
Code 26
3.5VF
Code 28
2.9 3.0 3.1 3.2
Code 32
3.3 3.4 3.5 3.6 3.7 3.8 3.9 4.0 4.1 4.2
3.2
3.3
3.4
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
(D1-D2 = 3.5V; D3-D4 = 3.2V)
100 90 5.0
Operating Current
(Code 23; EN_FLSH Off)
Code 26
Efficiency (%)
80
4.0 3.0 2.0 1.0
V_DX = 3.3V
60 50 40 30 2.9
Code 28
3.0 3.1 3.2
Code 32
3.3 3.4 3.5 3.6 3.7 3.8 3.9 4.0 4.1 4.2
IIN (A)
70
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)
Input Voltage (V)
Operating Current
(Code 23; EN_FLSH On; IOUT = 100mA)
8.0 7.0 6.0
V_DX = 3.3V
IIN (A)
5.0 4.0 3.0 2.0 1.0 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
V_DX = 3.0V
Input Voltage (V)
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Multi-Mode Charge Pump for White LED Backlight and Flash Applications Typical Characteristics-White LED Backlight Driver Section
VIN = 3.5V, CIN = 2.2F, CCP = C1 = C2 = 1.0F; TA = 25C, unless otherwise noted.
AAT2801
Turn-On to 1X Mode
(4x19mA Load) EN/SET (2V/div) VCP (4V/div) VDIODE (2V/div) IIN (100mA/div) EN/SET (2V/div) VCP (4V/div) VDIODE (2V/div) IIN (100mA/div)
Turn-On to 1X Mode
(4x30mA Load)
Time (100s/div)
Time (100s/div)
Turn-On to 1.5X Mode
(4x19mA Load) EN/SET (2V/div) VCP (4V/div) VDIODE (2V/div) IIN (100mA/div)
Turn-Off from Full-Scale 2X Mode
EN/SET (2V/div) VDIODE (2V/div) IIN (200mA/div)
Time (100s/div)
Time (100s/div)
Flash Section Turn-On
(VIN = 3.5V; IOUT = 100mA; EN/SET = GND)
Flash Section Turn-On
(VIN = 3.5V; IOUT = 200mA; EN/SET = GND)
EN_FLSH (2V/div) VOUT (2V/div) IIN (100mA/div)
EN_FLSH (2V/div) VOUT (2V/div) IIN (100mA/div)
Time (100s/div)
Time (100s/div)
6
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Multi-Mode Charge Pump for White LED Backlight and Flash Applications Typical Characteristics-White LED Backlight Driver Section
VIN = 3.5V, CIN = 2.2F, CCP = C1 = C2 = 1.0F; TA = 25C, unless otherwise noted.
AAT2801
Charge Pump to Load Switch
(1.5X Mode; 4x19mA Load) VIN (500mV/div) VCP (1V/div) VDIODE (500mV/div) IIN (50mA/div)
Charge Pump to Load Switch
(1.5X Mode; 4x30mA Load)
VIN (500mV/div) VCP (1V/div) VDIODE (500mV/div) IIN (50mA/div)
Time (5ms/div)
Time (5ms/div)
Charge Pump to Load Switch
(2X Mode; 4x19mA Load)
Charge Pump to Load Switch
(2X Mode; 4x30mA Load)
VIN (500mV/div) VCP (1V/div) VDIODE (500mV/div) IIN (50mA/div)
VIN (500mV/div) VCP (1V/div) VDIODE (500mV/div) IIN (50mA/div)
Time (5ms/div)
Time (5ms/div)
Load Switch to Charge Pump
(1.5X Mode; 4x19mA Load) VIN (1V/div) VCP (4V/div) VDIODE (500mV/div) IIN (50mA/div) VIN (1V/div) VCP (4V/div) VDIODE (500mV/div) IIN (50mA/div)
Load Switch to Charge Pump
(1.5X Mode; 4x30mA Load)
Time (2ms/div)
Time (2ms/div)
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Multi-Mode Charge Pump for White LED Backlight and Flash Applications Typical Characteristics-White LED Backlight Driver Section
VIN = 3.5V, CIN = 2.2F, CCP = C1 = C2 = 1.0F; TA = 25C, unless otherwise noted.
AAT2801
Line Response
(1X Mode; 4x19mA Load)
Line Response
(1X Mode; 4x30mA Load)
VIN (0.5V/div) VLED (20mV/div) VCP (0.5V/div) ID (10mA/div) Time (1ms/div)
VIN (0.5V/div) VLED (20mV/div) VCP (0.5V/div) ID (10mA/div) Time (1ms/div)
Line Response
(1.5X Mode; 4x19mA Load) VIN (0.5V/div) VDX (20mV/div) VCP (0.5V/div) IDX (10mA/div) Time (1ms/div)
Line Response
(1.5X Mode; 4x30mA Load)
VIN (0.5V/div) VLED (20mV/div) VCP (0.5V/div) ID (10mA/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)
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Multi-Mode Charge Pump for White LED Backlight and Flash Applications Typical Characteristics-White LED Backlight Driver Section
VIN = 3.5V, CIN = 2.2F, CCP = C1 = C2 = 1.0F; TA = 25C, unless otherwise noted.
AAT2801
Operating Characteristics
(I_DX = 4x15mA; 1.5X Mode) VIN = 3.0V VDX (20mV/div) IIN (10mA/div) VCP (20mV/div) VF (40mV/div)
Operating Characteristics
(I_DX = 4x15mA; 1.5X Mode; IOUT = 100mA) VIN = 3.0V
VDX (20mV/div)
IIN (10mA/div) VCP (20mV/div)
Time (1s/div)
Time (1s/div)
Operating Characteristics
(I_DX = 4x30mA; 1.5X Mode) VIN = 3.5V VDX (20mV/div) IIN (10mA/div) VCP (40mV/div) VDX (20mV/div) IIN (10mA/div) VCP (40mV/div) VF (40mV/div) Time (1s/div)
Operating Characteristics
(I_DX = 4x30mA; 1.5X Mode; IOUT = 100mA)
Time (1s/div)
Input Current vs. Input Voltage
(4x10mA)
90 80 70 60 300
Input Current vs. Input Voltage
(4x30mA)
VDIODE = 3.4V
250 200
VDIODE = 3.4V
IIN (mA)
50 40 30 20 10 0 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
IIN (mA)
VDIODE = 3.0V
150 100 50 0 2.7
VDIODE = 3.0V
3.1 3.5 3.9 4.3 4.7 5.1 5.5
Input Voltage (V)
Input Voltage (V)
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Multi-Mode Charge Pump for White LED Backlight and Flash Applications Typical Characteristics-White LED Backlight Driver Section
VIN = 3.5V, CIN = 2.2F, CCP = C1 = C2 = 1.0F; TA = 25C, unless otherwise noted.
AAT2801
Diode Current vs. Input Voltage
(30mA; 15mA settings)
40 35 0.850 0.825
VIH and VIL vs. VIN
VDIODE = 3.4V
0.800 0.775 0.750 0.725 0.700 0.675 0.650 0.625 0.600
IDIODE (mA)
30 25 20 15 10 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5
VIH VIL
VDIODE = 3.4V
2.5
3.0
3.5
4.0
4.5
5.0
5.5
Input Voltage (V)
Input Voltage (V)
10
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Multi-Mode Charge Pump for White LED Backlight and Flash Applications Typical Characteristics-Flash Driver Charge Pump Section
VIN = 3.5V, CIN = 2.2F, C3 = CF = 1.0F, TA = 25C, unless otherwise noted.
AAT2801
Output Voltage vs. Output Current
5.0 4.8 4.6 4.4 4.2 4.0 3.8 3.6 3.4 3.2 3.0 0 40 80 120 160 200
Efficiency vs. Supply Voltage
100 90 80 50mA
Output Voltage (V)
VIN=3.3
VIN=3.6
Efficiency (%)
70 60 50 40 30 20 10 0 2.7 3.0 3.3 3.6 3.9 4.2 4.5 100mA 150mA
VIN = 2.7
VIN = 3.0
Output Current (mA)
Supply Voltage (V)
Efficiency vs. Load Current
Maximum Current Pulse (mA)
100 90 80 VIN = 2.7V VIN = 3.0V
Maximum Current Pulse vs. Supply Voltage
600 500 400 300 200 100 0 3.0 3.2 3.4 3.6 3.8 4.0 4.2 One-shot pulse duration = 250ms VOUT> 4.0V
Efficiency (%)
70 60 50 40 30 20 10 0 0.1 1.0 10 100 1000 VIN = 3.3V VIN = 3.6V
Load Current (mA)
Supply Voltage (V)
Load Response
(100mA Load) VIN = 3.5V VOUT (10mV/div) VOUT (10mV/div) VIN = 3.5V
Load Response
(50mA Load)
IOUT (50mA/div)
IOUT (20mA/div)
Time (5ms/div)
Time (5ms/div)
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Multi-Mode Charge Pump for White LED Backlight and Flash Applications Typical Characteristics-Flash Driver Charge Pump Section
VIN = 3.5V, CIN = 2.2F, C3 = CF = 1.0F, TA = 25C, unless otherwise noted.
AAT2801
Startup
1.00 0.95
VEN Threshold vs. Supply Voltage
VEN Threshold (V)
ENABLE (1V/div)
0.90 0.85 0.80 0.75 0.70 0.65 0.60 0.55 0.50 2.7 3.1
ILOAD = 150mA @ VIN = 3.3V ILOAD = 100mA @ VIN = 3.0V
VIH VIL
VOUT (1V/div)
ILOAD = 150mA @ VIN = 3.3V
3.5
3.9
4.3
4.7
5.1
5.5
Time (100s/div)
Supply Voltage (V)
Normalized Output Voltage vs. Temperature
Normalized Output Voltage (%)
2.0 1.5 1.0 0.5 0.0 -0.5 -1.0 -1.5 -2.0 -50 -30 -10 10 30 50 70 90
IOUT = 25mA
Temperature (C)
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Multi-Mode Charge Pump for White LED Backlight and Flash Applications Functional Block Diagram
C3 + C3 -
AAT2801
2X CP Soft Start
OUT_FLSH
EN_FLSH
1MHz Oscillator
IN
VREF Soft-Start Control 1MHz Oscillator Voltage Reference
C1+
1X 1.5X 2X Charge Pump
C1C2+ C2CP D1 D2 D3 D4
D/A
EN/SET
Control Logic
D/A D/A D/A
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
Multi-Mode Charge Pump for White LED Backlight and Flash Applications
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.
AAT2801
Applications Information-- White LED Backlight Section
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. 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 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.
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. The AAT2801 requires only six external components: three 1F ceramic capacitors for the charge pump flying capacitors (C1, C2 and C3), one 1F ceramic input capacitor (CIN), one 1F ceramic charge pump output capacitor (CCP), and one 1F 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.
Normalized Current Level Settings
1.00
Current (mA)
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
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Multi-Mode Charge Pump for White LED Backlight and Flash Applications
Constant Current Source Output Nominal Programming Levels (mA)
Code
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
AAT2801
S2Cwire Serial Interface
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 1A from VIN. The internal data register is reset to 0 during shutdown.
IOUT (typ) (mA)
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
Code
17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
IOUT (typ) (mA)
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
S2Cwire Serial Interface Timing Diagram
THI TLO TLAT TOFF
EN/SET
1 2 n-1 n <= 32
Data Reg
0
n
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
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.
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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.
AAT2801
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:
=
POUT PIN
The expression to define the ideal efficiency () can be rewritten as:
POUT VOUT x IOUT VOUT = = PIN VIN x IOUT VIN
=
-or VOUT VIN
(%) = 100
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 () 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 () for an ideal 1.5X charge pump can typically be expressed as the output power divided by the input power.
=
POUT PIN
16
2801.2006.04.1.3
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 () can be rewritten as:
VOUT x IOUT VOUT POUT = = PIN VIN x 1.5IOUT 1.5VIN
AAT2801
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 2.2F 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.
-or VOUT 1.5VIN
(%) = 100
For the voltage doubling charge pump mode, the expression to define the ideal efficiency () can be rewritten as:
V POUT VOUT x IOUT = = OUT PIN VIN x 2IOUT 2VIN
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.
=
-or VOUT (%) = 100 2VIN
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.
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 100m. A value of 1F 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
17
Multi-Mode Charge Pump for White LED Backlight and Flash Applications
C3 1F
AAT2801
C3+ VIN IN
C3-
4.5V CF 1F
OUT_FLSH
CIN 1F
AAT2801
RB Flash Enable
EN_FLSH
Flash LED
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:
(VOUT - VF) IF
applications. The device start-up time into a maximum load is about 200s, thus eliminating the need for pre-flash control synchronization. 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
RB =
RL =
Where: RB = Flash ballast resistor value in ohms () Regulated charge pump output voltage (typically 4.5V) Flash LED forward voltage at the desired forward current Desired flash LED forward current VOUT = VF IF = =
Where: RL = Light mode ballast resistor value in ohms () Regulated charge pump output voltage (typically 4.5V) Flash LED forward voltage at the desired forward current Desired flash LED forward current in the "light" mode
VOUT = VF IF = =
The flash LED function can be controlled by the AAT2801 flash enable (EN_FLSH) pin in most
18
2801.2006.04.1.3
Multi-Mode Charge Pump for White LED Backlight and Flash Applications
C3 1F
AAT2801
C3+ VIN CIN 1F IN
C3-
4.5V COUT 1F
OUT_FLSH
AAT2801
Flash Enable EN_FLSH RL RB
Flash LED
Flash Enable
Figure 2: Flash LED Driver with Gated Flash Application.
RB =
(VOUT - VF) - RDS IF
Where: RB RDS = = Flash ballast resistor value in ohms () Flash gating mosfet on resistance Regulated charge pump output voltage (typically 4.5V) Flash LED forward voltage at the desired forward current Desired flash LED forward current
VOUT = VF IF = =
2801.2006.04.1.3
19
Multi-Mode Charge Pump for White LED Backlight and Flash Applications Ordering Information
Output Voltage
4.5V 5.0V
AAT2801
Package
TDFN44-16 TDFN44-16
Marking1
MSXYY
Part Number (Tape and Reel)2
AAT2801IXN-4.5-T1 AAT2801IXN-5.0-T1
Package Information
Index Area (D/2 x E/2) Detail "B"
4.00 0.05
3.30 0.05
0.3 0.10 0.16
0.375 0.125
0.075 0.075 0.1 REF Detail "A"
Top View
Bottom View
Pin 1 Indicator (optional)
7.5 7.5
+ 0.05 0.8 -0.20
0.229 0.051
Detail "B"
Option A: C0.30 (4x) max Chamfered corner Option B: R0.30 (4x) max Round corner
0.05 0.05
Side View
All dimensions in millimeters.
Detail "A"
1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD.
(c) 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
0.23 0.05
0.45 0.05
4.00 0.05
2.60 0.05

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