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AAT2806

Dual High Efficiency Charge Pump for White LED and Flash Applications General Description

AAT2806
Dual High Efficiency Charge Pump for White LED and Flash Applications General Description
Features
ChargePumpTM
VIN Range: 2.7V to 5.5V Dual Charge Pump to Support Backlight and Flash LEDs Backlight Charge Pump: - Regulated Current - Four Current Sink Inputs - S2Cwire Brightness Control - Tri-Mode Charge Pump - Maximum 20mA of Current Per Input - Low IQ (50µA) in Light Load Mode Flash Charge Pump: - Regulated Output Voltage - Up to 250mA of Pulsed Current Independent Backlight / Flash Control Low Noise 1MHz Constant Frequency Operation Automatic Soft Start No Inductors Available in TDFN44-16 Package
Applications
· · · Color (RGB) Lighting White LED Backlighting White LED Photo Flash
Typical Application
AAT2806
Backlight
COUT 1F
AAT2806
Dual High Efficiency Charge Pump for White LED and Flash Applications Pin Descriptions
Symbol
Function
Flying capacitor 3 negative terminal. Flying capacitor 3 positive terminal. Connect a 1µF capacitor between C3+ and C3-. Regulated output voltage for the flash LED. Requires 1µF capacitor connected between this pin and ground. Input power supply. Requires 1µF capacitor connected between this pin and ground. Current sink input 4. Current sink input 3. Current sink input 2. Current sink input 1. Ground. S2Cwire serial interface control pin. It is used to enable / disable the backlight charge pump and to control the brightness of the white LEDs. Flying capacitor 1 positive terminal. Connect a 1µF capacitor between C1+ and C1-. Flying capacitor 1 negative terminal. Regulated output voltage for the white LEDs. Requires 1µF capacitor connected between this pin and ground. Flying capacitor 2 positive terminal. Connect a 1µF capacitor between C2+ and C2-. Flying capacitor 2 negative terminal. Enable / disable pin for the flash charge pump. Exposed paddle (bottom) connect to GND directly beneath package.
Pin Configuration
TDFN44-16 (Top View)
AAT2806
Dual High Efficiency Charge Pump for White LED and Flash Applications Absolute Maximum Ratings1
Symbol
Description
Value
-0.3 to 6.0 -0.3 to VIN + 0.3 300
Units
Thermal Information2
Symbol
Description
Maximum Power Dissipation Maximum Thermal Resistance
Value
Units
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. 2806.2007.09.1.9
AAT2806
Dual High Efficiency Charge Pump for White LED and Flash Applications Electrical Characteristics1
Description
Operation Range
Conditions
Min Typ Max Units
Input Power Supply
1. The AAT2806 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. Specification applies only to the tri-mode charge pump. 3. Determined by the average of all active channels. 4. Current matching is defined as the deviation of any sink current from the average of all active channels. 5. Specification applies only to the charge pump doubler.
AAT2806
Dual High Efficiency Charge Pump for White LED and Flash Applications Typical Characteristics- Flash Driver Charge Pump Section
Output Voltage vs. Output Current
Maximum Current Pulse vs. Supply Voltage
Maximum Current Pulse (mA)
Output Voltage (V)
Output Current (mA)
Supply Voltage (V)
Load Response vs. Time
IOUT (20mA / div)
IOUT (50mA / div)
Time (5ms / div)
Output Ripple Voltage vs. Time
IIN (10mA / div)
Time (500ns / div)
AAT2806
Dual High Efficiency Charge Pump for White LED and Flash Applications Typical Characteristics- Flash Driver Charge Pump Section
Supply Current vs. Supply Voltage
Oscillator Frequency vs. Supply Voltage
Oscillator Frequency (MHz)
Supply Current (mA)
+25°C
+85°C -40°C
Supply Voltage (V)
AAT2806
Dual High Efficiency Charge Pump for White LED and Flash Applications Typical Characteristics- White LED Backlight Driver Section
Turn-On to 1X Mode
Turn-On to 1.5X Mode
EN (2V / div) CP (2V / div) VSINK (500mV / div) IIN (200mA / div) Time (100µs / div)
EN (2V / div) CP (2V / div) VSINK (500mV / div) IIN (200mA / div)
Time (100µs / div)
Turn-On to 2X Mode
Turn-Off from 1.5X Mode
EN (2V / div) CP (2V / div) VSINK (500mV / div) IIN (200mA / div)
IIN (100mA / div)
Time (100µs / div)
Time (500µs / div)
Efficiency vs. Supply Voltage
Current Matching vs. Temperature
Channel 2 Channel 4 Channel 3 Channel 1
Current (mA)
Supply Voltage (V)
Temperature (°C) °
AAT2806
Dual High Efficiency Charge Pump for White LED and Flash Applications Typical Characteristics- White LED Backlight Driver Section
Load Characteristics
VIN (40mV / div) CP (40mV / div)
VSINK (40mV / div)
Time (500ns / div)
Load Characteristics
VIN (40mV / div) CP (40mV / div) VSINK (40mV / div)
Time (500ns / div)
EN / SET Latch Timeout vs. Input Voltage
EN / SET Latch Timeout (s)
EN / SET Off Timeout vs. Input Voltage
EN / SET Off Timeout (s)
-40°C
Input Voltage (V)
AAT2806
Dual High Efficiency Charge Pump for White LED and Flash Applications Typical Characteristics- White LED Backlight Driver Section
Input Ripple vs. Input Voltage
Enable Threshold High (V)
Enable Threshold High vs. Input Voltage
Amplitude (mV)
-40°C
Input Voltage (V)
Enable Threshold Low vs. Input Voltage
Enable Threshold Low (V)
-40°C
Input Voltage (V)
AAT2806
Dual High Efficiency Charge Pump for White LED and Flash Applications Functional Block Diagram
Soft-Start
1MHz Oscillator
2X Charge Pump
VREF Soft-Start Control 1MHz Oscillator Voltage Reference D / A 6 x 16 Bit ROM D / A D / A 1X 1.5X 2X Charge Pump
Control Logic
Functional Description
The AAT2806 is a dual charge pump designed for flash and white LED applications. The backlight charge pump 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 voltage discharges over time, the white LED charge pump is enabled when any of the four current sink
AAT2806
Dual High Efficiency Charge Pump for White LED and Flash Applications
The flash charge pump is a charge pump doubler with regulated output voltage. It is designed to deliver 120mA of continuous current and 250mA of pulsed current. The AAT2806 requires 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 capacitor (COUT), and one 1µF ceramic capacitor for the flash charge pump output capacitor (COUT). IOUT (mA) D1-D3 Sub-Group D4
Constant Current Output Level Settings
Table 1: Constant Current Programming Levels.
S2Cwire Serial Interface
AAT2806
Dual High Efficiency Charge Pump for White LED and Flash Applications
S2Cwire Serial Interface Timing Diagram
T HI TLO TLAT TOFF
Data Reg
Disabled Current Sinks
The backlight charge pump is equipped with an auto-disable 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 10µA.
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 AAT2806 make it capable of driving LEDs with forward voltages as high as 4.3V 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 AAT2806 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-to-peak, typically ten times less than inductor-based DC / DC boost converter white LED backlight solutions. The AAT2806 soft-start feature prevents noise transient effects associated with inrush currents during start-up of the charge pump circuit.
Applications Information
LED Selection
The AAT2806 is specifically intended for driving white LEDs. However, the device design will allow the AAT2806 to drive most types of LEDs with forward voltage specifications ranging from 2.0V to 4.3V. LED applications may include main 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. Since the D1 to D4 input current sinks are matched with negligible voltage dependence, the LED brightness will be matched regardless of the specific LED forward voltage (VF) levels.
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 100m. A value of 1µF for all six capacitors is a good starting point when choosing capacitors.
AAT2806
Dual High Efficiency Charge Pump for White LED and Flash Applications
Capacitor Characteristics
Ceramic composition capacitors are highly recommended over all other types of capacitors for use with the AAT2806. 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.
Charge Pump Power Efficiency
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.
Ceramic Capacitor Materials
Ceramic capacitors less than 0.1µF are typically made from NPO or C0G materials. NPO and C0G materials generally have tight tolerance and are very stable over temperature. Larger capacitor values are usually composed of X7R, X5R, Z5U, or Y5V dielectric materials. Large ceramic capacitors (i.e., greater than 2.2µF) are often available in lowcost Y5V and Z5U dielectrics, but capacitors greater than 1µF are not typically required for AAT2806 applications. 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.
Thermal Protection
The AAT2806 has a thermal protection circuit that will shut down the two charge pumps if the die temperature rises above the thermal limit.
POUT PIN
AAT2806
Dual High Efficiency Charge Pump for White LED and Flash Applications
The expression to define the ideal efficiency () can be rewritten as:
Charge Pump Mode Efficiency: Fractional charge pumps 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 a 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:
-or VOUT 2.0VIN
POUT PIN
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:
-or VOUT 1.5VIN
AAT2806
Dual High Efficiency Charge Pump for White LED and Flash Applications Ordering Information
Package
TDFN44-16
Marking1
NPXYY
Part Number (Tape and Reel)2
AAT2806IXN-4.5-T1
Package Information
TDFN44-16
Index Area (D / 2 x E / 2) Detail "B"
Top View
Bottom View
Pin 1 Indicator (optional)
Detail "B"
Option A: C0.30 (4x) max Chamfered corner Option B: R0.30 (4x) max Round corner
Side View Detail "A"
All dimensions in millimeters.
AAT2806
Dual High Efficiency Charge Pump for White LED and Flash Applications
Advanced Analogic Technologies, Inc.
3230 Scott Boulevard, Santa Clara, CA 95054 Phone (408) 737- 4600 Fax (408) 737- 4611 16