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AAT3120
3-Channel Charge Pump For White LED Applications General Description
The AAT3120 is a low noise, constant frequency charge pump DC/DC converter that uses fractional (1.5X) conversion to improve efficiency for white LED applications. The device can be used to produce eight current levels up to 20mA per channel for up to three channels. 1X load switch mode is also built-in to improve efficiency at low current settings. Low external parts count (two 1F flying capacitors and two small 1F capacitors at VIN and OUT) makes the AAT3120 ideally suited for small battery-powered applications. AnalogicTech's S2CwireTM (Simple Serial ControlTM) serial digital input is used to enable, disable, and set current for each LED at eight different levels. The AAT3120 has a thermal management system to protect the device in the event of a short-circuit condition at the output pin. Built-in soft-start circuitry prevents excessive inrush current during startup. A high charge pump switching frequency enables the use of very small external capacitors. A low current shutdown feature disconnects the load from VIN and reduces quiescent current to less than 1A. The AAT3120 is available in the very small Pb-free 12-pin TSOPJW package.
Features
* * * *
ChargePumpTM
* * * * * * *
VIN Range: 2.7V to 5.5V Fractional Charge Pump Mode Drives Low-VF and High-VF Type LEDs Up to Three LED Outputs -- Single Wire Programming -- Eight Regulated Current Settings -- Max 20mA per Channel Low Noise Constant Frequency Operation No Inductors 1MHz Switching Frequency Small Application Circuit Automatic Soft-Start IQ <1A in Shutdown 12-Pin TSOPJW Package
Applications
* * * * Color (RGB) Lighting Programmable Current Source White LED Backlighting White Photo Flash for DSCs
Typical Application
VIN C1+ C1 1F VOUT VBATTERY CIN 1F C OUT 1F C1C2+ C2 1F
AAT3120
C2D1 D2 D3
EN/SET
EN/SET GND
D3
D2
D1
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AAT3120
3-Channel Charge Pump For White LED Applications Pin Descriptions
Pin #
1 2 3 4 5 6 7 8 9 10 11 12
Symbol
C2+ OUT C1C1+ N/C D3 D2 D1 EN/SET IN GND C2-
Function
Flying capacitor 2 positive terminal. Connect a 1F capacitor between C2+ and C2-. Charge pump output. Requires 1F capacitor connected between this pin and ground. Flying capacitor 1 negative terminal. Flying capacitor 1 positive terminal. Connect a 1F capacitor between C1+ and C1-. No connection. Current source output #3. Current source output #2. Current source output #1. Control pin. Input power supply. Requires 1F capacitor connected between this pin and ground. Ground. Flying capacitor 2 negative terminal.
Pin Configuration
TSOPJW-12 (Top View) C2+ OUT C1C1+ N/C D3 C2GND IN EN/SET D1 D2
1 2 3 4 5 6
12 11 10 9 8 7
2
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AAT3120
3-Channel Charge Pump For White LED Applications Absolute Maximum Ratings1
TA = 25C, unless otherwise noted. Symbol
VIN VOUT VEN/SET VEN/SET(MAX) IOUT2 TJ TLEAD
Description
Input Voltage Charge Pump Output FB or EN/SET to GND Voltage Maximum EN/SET to Input Voltage Maximum DC Output Current Operating Junction Temperature Range Maximum Soldering Temperature (at leads, 10 sec)
Value
-0.3 to 6 -0.3 to 6 -0.3 to 6 0.3 150 -40 to 150 300
Units
V V V V mA C C
Thermal Information3
Symbol
JA PD
Description
Thermal Resistance Maximum Power Dissipation4
Value
160 0.625
Units
C/W 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. 3120.2005.11.1.1
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AAT3120
3-Channel Charge Pump For White LED Applications Electrical Characteristics1
CIN = COUT = C1 = C2 = 1.0F; TA = -40C to +85C, unless otherwise noted. Typical values are TA = 25C, VIN = 3.5V. Symbol Description Conditions Min
2.7 3.0V VIN 5.5V, Active, No Load Current EN = 0 3.0 VIN 5.5 VD1:D3 = 3.6, VIN = 3.5V 1.8
Typ
Max Units
5.5 3.0 1.0 22 V mA A mA %
Input Power Supply VIN Operation Range ICC Operating Current Shutdown Current Output Current I(D-Match) Current Matching Between Any Two Outputs Charge Pump Section TSS Soft-Start Time FCLK Clock Frequency EN/SET VEN(L) Enable Threshold Low VEN(H) Enable Threshold High TEN/SET LO EN/SET Low Time TEN/SET HI Minimum EN/SET High Time TOFF EN/SET Off Timeout Input Current EN/SET Input Leakage ISHDN IDX
18
20 0.5
200 1000 2.7V VIN 5.5V 2.7V VIN 5.5V 0.4 1.4 0.3 50 -1 500 1 75
s kHz V V s ns s A
1. The AAT3120 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.
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AAT3120
3-Channel Charge Pump For White LED Applications Typical Characteristics
Turn-On to Full-Scale Load Switch
ENSET (2V/div)
Turn-On to Full-Scale Charge Pump
ENSET (2V/div)
CP (2V/div) VDIODE (2V/div) IIN (200mA/div) Time (100s/div)
CP (2V/div) VDIODE (2V/div) IIN (200mA/div) Time (100s/div)
Turn-Off from Full-Scale Charge Pump
65
IDIODE vs. Input Voltage
(3x20mA)
ENSET (2V/div) IDIODE (mA)
62 59 56 53
VF = 3.4V
VDIODE (2V/div)
VF = 3.0V
VF = 3.2V
IIN (100mA/div)
50 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
Input Voltage (V) Time (400s/div)
IDIODE vs. Input Voltage
(3x8.3mA)
30 27
VF = 3.4V
IDIODE (mA)
24 21 18 15 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
VF = 3.0V
VF = 3.2V
Input Voltage (V)
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AAT3120
3-Channel Charge Pump For White LED Applications Typical Characteristics
Efficiency vs. Input Voltage
(3x20mA)
95 90 95
Efficiency vs. Input Voltage
(3x8.3mA) VF = 3.0V VF = 3.2V VF = 3.4V
VF = 3.0V
VF = 3.2V
VF = 3.4V Efficiency (%)
90 85 80 75 70 65 60 55
Efficiency (%)
85 80 75 70 65 60 55 50 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
50 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
Input Voltage (V)
Input Voltage (V)
60mA Load Characteristics
Charge Pump to Load Switch (60mA)
VIN (20mV/div) OUT (20mV/div)
VIN (10mV/div) OUT (2V/div) VDIODE (2V/div)
VDIODE (20mV/div) Time (500ns/div)
IIN (100mA/div) Time (100s/div)
Load Switch to Charge Pump (60mA)
VIN (10mV/div) OUT (2V/div) VDIODE (2V/div) IIN (100mA/div) Time (100s/div)
6
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AAT3120
3-Channel Charge Pump For White LED Applications Functional Block Diagram
VIN
Soft-Start Control 1MHz Oscillator Voltage Reference 1X / 1.5X Charge Pump
C1+ C1C2+ C2-
OUT
D1
Current Reference Quad Output DAC
D2 D3
EN/SET
Single-Wire Interface
32 x 16 bit ROM
GND
Functional Description
The AAT3120 is a dual mode load switch (1X) and high efficiency (1.5X) fractional charge pump device intended for white LED backlight applications. The fractional charge pump consists of a low dropout linear voltage regulator followed by a 1.5X charge pump with multiple current source outputs. To maximize power conversion efficiency, an internal feedback control sensing circuit monitors the voltage required on the constant current source outputs. This control circuit then sets the load switch and charge pump functions based upon the input voltage level versus the output voltage level needed. The 1X load switch / 1.5X charge pump mode is decided on the voltage sensed on the output D1. Switchover between the 1.5X (chargepump) operating mode and the 1X (load switch) mode occurs automatically (as a function of input and output voltages) and does not require user intervention to maintain maximum efficiency.
The AAT3120 requires only four external components: two 1F ceramic capacitors for the charge pump flying capacitors (C1 and C2), one 1F ceramic input capacitor (CIN), and one 0.33F to 1F ceramic output capacitor (COUT). The LDO / 1.5X charge pump output is converted into three (D1 to D3) constant current outputs to drive three individual LEDs with a maximum current of 20mA each. The current source output magnitude is controlled by the EN/SET serial data single-wire interface. The interface records rising edges of the EN/SET pin and decodes them into eight individual current level settings (see Table 1, Current Level Settings). Once the final clock cycle is input for the desired brightness level, the EN/SET pin is held high to maintain the device output current at the programmed level. The device is disabled 500s after the EN/SET pin transitions to a logic low state.
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AAT3120
3-Channel Charge Pump For White LED Applications
pin and decodes them into eight individual current level settings. Code 8 is full scale. The counter can be clocked at speeds up to 1MHz, so intermediate states are not visible. The first rising edge of EN/SET enables the IC and initially sets the output LED current to zero. The next lowest setting is equal to 525A. Once the final clock cycle is input for the desired brightness level, the EN/SET pin is held high to maintain the device output current at the programmed level. The device is disabled 500s after the EN/SET pin transitions to a logic low state. The EN/SET timing is designed to accommodate a wide range of data rates. After the first rising edge of EN/SET, the charge pump is enabled and reaches full capacity after the soft-start time (TSS). During the soft-start time, multiple clock pulses may be entered on the EN/SET pin to set the final output current level with a single burst of clocks. Alternatively, the EN/SET clock pulses may be entered one at a time to gradually increase the LED brightness over any desired time period. A constant current is sourced as long as EN/SET remains in a logic high state. The current source outputs are switched off after EN/SET has remained in a low state for at least the TOFF timeout period.
Code
1 2 3 4 5 6 7 8
IOUT, Each LED (mA)
0 0.5 1.3 3.3 8.3 11.1 15 20
Table 1: Current Level Settings.
Constant Current Output Level Settings
The constant current source output amplitude for output D1 to D3 is set via the serial interface. Because the outputs D1 to D3 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 AAT3120 is programmable through its simple single-wire serial interface, 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."
Test Current/Channel Disable
Each channel of the output is equipped with a test current function. A small amount of current (~2A) is injected into each output current source to detect the presence of load (LED). For unused channels that are tied to ground or load LED fail short, those channels will be automatically disabled instead of wasting the programmed output current.
EN/SET Serial Interface
The current source output magnitude is controlled by the EN/SET serial data single-wire interface. The interface records rising edges of the EN/SET
EN/SET Timing
tHI tLO tOFF
EN/SET Code
OFF
1
2
3
OFF
8
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AAT3120
3-Channel Charge Pump For White LED Applications Applications Information
LED Selection
The AAT3120 is specifically intended for driving white LEDs. However, the device design will allow the AAT3120 to drive most types of LEDs with forward voltage specifications ranging from 2.0V to 4.3V. LED applications may include main and subLCD 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 D3 output current sources are matched with negligible voltage dependence, the LED brightness will be matched regardless of the specific LED forward voltage (VF) levels. 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-sources in the AAT3120 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. Since the AAT3120 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 D3) 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. The AAT3120 efficiency may 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 D3 for a given constant current setting. Depending upon the case of VIN being greater than the specific voltage seen across the load on D1, the device will operate in "load switch" mode. If the voltage seen on the constant current source output is less than VIN, then the device will operate in 1.5X charge pump mode. Each of these two modes will yield different efficiency values. One should refer to the following two sections for explanations of each operational mode.
Device Switching Noise Performance
The AAT3120 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 AAT3120 soft-start feature prevents noise transient effects associated with in-rush currents during start up of the charge pump circuit.
Load Switch Mode Efficiency
The AAT3120 load switch mode is operational at all times. It functions alone to enhance device power conversion efficiency when the condition exists where VIN is greater than the voltages at 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
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 AAT3120, it is very difficult to measure efficiency in terms of a percent value comparing input power over output power. =
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AAT3120
3-Channel Charge Pump For White LED Applications
The expression to define the ideal efficiency () can be rewritten as: POUT VOUT x IOUT VOUT = = PIN VIN x IOUT VIN close agreement for output load conditions from 1mA to 100mA. Efficiency will decrease as load current drops below 0.05mA or when level of VIN approaches VOUT. Refer to the Typical Characteristics section of this document for measured plots of efficiency versus input voltage and output load current for the given charge pump output voltage options.
= -or-
(%) = 100
VOUT VIN
Ballast Resistors for Current Matching
In some applications, white LED forward voltages can vary significantly. Ballast resistors between the LED cathodes and ground are recommended for balancing the forward voltage differences. The ballast resistor value may be approximated by the following equation: VSOURCE - VF IF
Charge Pump Section Efficiency
The AAT3120 contains a fractional 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 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
RB =
Capacitor Selection
Careful selection of the four external capacitors CIN, C1, C2, and COUT 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 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.
=
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: POUT VOUT x IOUT VOUT = = PIN VIN x 1.5IOUT 1.5VIN
= -or-
Capacitor Characteristics
Ceramic composition capacitors are highly recommended over all other types of capacitors for use with the AAT3120. 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.
(%) = 100
VOUT 1.5VIN
For a charge pump with an output of 5 volts and a nominal input of 3.5 volts, the theoretical efficiency is 95%. Due to internal switching losses and IC quiescent current consumption, the actual efficiency can be measured at 93%. These figures are in
Equivalent Series Resistance
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AAT3120
3-Channel Charge Pump For White LED Applications
ESR is an important characteristic to consider when selecting a capacitor. ESR is a resistance internal to a capacitor, which 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. 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 AAT3120 has a thermal protection circuit that will shut down the internal LDO and charge pump if the die temperature rises above the thermal limit, as is the case during a short circuit of the OUT pin.
Ceramic Capacitor Materials
Ceramic capacitors less than 0.1F are typically made from NPO or C0G materials. NPO and C0G materials typically have tight tolerance and are stable over temperature. Large capacitor values are typically composed of X7R, X5R, Z5U, or Y5V dielectric materials. Large ceramic capacitors, typically greater than 2.2F, are often available in lowcost Y5V and Z5U dielectrics, but capacitors greater than 1F are typically not required for AAT3120 applications.
Charge Pump Compatibility
The AAT3120 is pin-compatible with the AAT3113 in TSOPJW-12 packages, with no D4 output. Compared to the AAT3113, the AAT3120 offers an improved overall efficiency, wider operating range, and the ability to drive high-VF type LEDs (up to 4.3V) at full current from a 3V input condition. The AAT3120 is well suited for battery-powered applications using single-cell Lithium-Ion (Li-Ion) batteries (4.2V to 2.8V), Lithium Polymer batteries, and 3-series connected dry cells (3.6V).
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AAT3120
3-Channel Charge Pump For White LED Applications Additional Application Circuits
VIN C1+ C1 1F VOUT VBATTERY C IN 1F COUT 1F C1C2+ C2 1F
AAT3120
C2D1 D2 D3
Display Module
EN/SET
EN/SET GND
D1
D2
D3
R
R
R
AAT3120 Driving a Display Module with Three Paralleled White LEDs.
VIN
C1+ C1 1F
VOUT VBATTERY CIN 1F C OUT 1F
C1C2+ C2 1F Common-Anode RGB Color LED
AAT3120
C2D1 D2 D3
EN/SET
EN/SET GND
RED
GRN
BLU
R
R
R
Enable Red Enable Green Enable Blue
AAT3120 Driving Common-Anode RGB Color LED.
12
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AAT3120
3-Channel Charge Pump For White LED Applications Ordering Information
Package
TSOPJW-12
Marking1
NGXYY
Part Number (Tape and Reel)2
AAT3120ITP-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 Information
0.10 0.20 + 0.05 -
2.40 0.10
0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC 0.50 BSC
2.85 0.20
7 NOM 3.00 0.10
0.9625 0.0375 + 0.10 1.00 - 0.065
0.04 REF 0.15 0.05 4 4
0.010
0.055 0.045
0.45 0.15 2.75 0.25
All dimensions in millimeters.
1. XYY = assembly and date code. 2. Sample stock is generally held on part numbers listed in BOLD. 3120.2005.11.1.1
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AAT3120
3-Channel Charge Pump For White LED Applications
(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.
Advanced Analogic Technologies, Inc.
830 E. Arques Avenue, Sunnyvale, CA 94085 Phone (408) 737-4600 Fax (408) 737-4611 14
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