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High Efficiency 1.5X Fractional Charge Pump for White LED Applications General Description
The AAT3132 is a low noise, constant frequency charge pump DC/DC converter that uses fractional (1.5X) conversion to maximize efficiency for White LED applications. The device can be used to produce current levels up to 20mA in three of its outputs, and up to 25 or 30mA in one of its outputs to drive LEDs from a 2.7V to 5.5V input. Outputs may be operated individually or paralleled for driving higher-current LEDs. Low external parts count (two 1F flying capacitors and two small 1F capacitors at VIN, and OUT) make the AAT3132 ideally suited for small battery-powered applications. AnalogicTechTM's Simple Serial ControlTM (S2CwireTM) interface is used to enable, disable and set the LED drive current in two groups: the three 20mA outputs and the single 30mA output with multiple level logarithmic scales. The AAT3132 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 start-up. 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 AAT3132 is available in very small 12 pin TSOPJW12 package.
AAT3132
Features
* * * * * * * * * * * * * * *
ChargePumpTM
VIN Range: 2.7 - 5.5 Volts < 1.0A of Shutdown current 1.0 MHz Switching Frequency White LED Backlighting Fully Independent Display Lighting Drives Low-VF & High-VF Type LEDs Up to three 20mA Outputs Single 25 or 30mA Output Multi Position Logarithmic Scale with Digital Control Low Noise Constant Frequency Operation Regulated Output Current Automatic Soft-Start No Inductors -40 to +85C Temperature Range 12 pin TSOPJW-12 package
Applications
* * * * White LED Backlighting White Photo-Flash for DSC's Color (RGB) Lighting Programmable Current Source
Typical Application
VIN C1+ C1 1F VOUT VBATTERY CIN 1F COUT 1F C1C2+ C2 1F
AAT3132
C2D1 D2 D3 D4
EN/SET
EN/SET D5 GND D4 D3 D2 D1
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High Efficiency 1.5X Fractional Charge Pump for White LED Applications Pin Descriptions
Pin #
1 2 3 4 5 6 7 8 9 10 11 12
AAT3132
Symbol
C2+ OUT C1C1+ D3 D2 D4 D1 EN/SET IN GND C2-
Function
Flying Capacitor 2 + terminal. Connect a 1F capacitor between C2+ and C2-. Charge pump output. Requires 1F capacitor connected between this pin and ground. Flying Capacitor 1 - terminal Flying Capacitor 1 + terminal. Connect a 1F capacitor between C1+ and C1-. Current source output #3 Current source output #2 Current source output #4 Current source output #1 Control Pin Input power supply. Requires 1F capacitor connected between this pin and ground. Ground Flying Capacitor 2 - terminal
Pin Configuration
TSOPJW-12 (Top view) C2+ OUT C1C1+ D3 D2 C2GND IN EN/SET D1 D4
1 2 3 4 5 6
12 11 10 9 8 7
2
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High Efficiency 1.5X Fractional Charge Pump for White LED Applications Absolute Maximum Ratings1
Symbol
VIN VOUT FB, VEN/SET VEN/SET(MAX) IOUT (2) TJ
AAT3132
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
Value
-0.3 to 6 -0.3 to 6 -0.3 to 6 VIN - 0.3 150 -40 to 150
Units
V V V V mA C
Notes: 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.
Thermal Information
Symbol
JA PD
Description
Thermal Resistance Maximum Power Dissipation (TA = 25C)
3 3, 4
Value
160 625
Units
C/W mW
Note 3: Mounted on a FR4 board. Note 4: Derate 6.25mW/C above 25C.
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High Efficiency 1.5X Fractional Charge Pump for White LED Applications Electrical Characteristics1
VIN = 3.5V, CIN = COUT = C1 = C2 = 1.0F; TA = -40 to 85C unless otherwise noted. Typical values are TA = 25C. Symbol Description Conditions Min
2.7 3.0 VIN 5.5, Active, No Load Current EN = 0 3.0 VIN 5.5 TA = 25C AAT3132-1 TA = 25C AAT3132 VD1:D3 = 3.6, VIN = 3.3V VIN = 3.5V, IOUT(TOTAL) = 90mA, Measured from IN to OUT 1.8
AAT3132
Typ
Max
5.5 3.5 1.0 22 27.5 33
Units
V mA A mA mA % %
Input Power Supply VIN Operation Range ICC Operating Current ISHDN IDX IDX I(D-Match) CP Charge Pump TSS FCLK EN/SET VEN(L) VEN(H) TEN/SET LO TEN/SET HI TOFF Input Current Shutdown Current Max. Output Current D1 to D3 Max. Output Current D4 Current Matching between any two outputs Charge Pump Section Efficiency Section Soft start time Clock Frequency Enable Threshold Low Enable Threshold High EN/SET low time Minimum EN/SET high time EN/SET Off Timeout EN/SET input leakage
18 22.5 27
20 25 30 0.5 93
200 1000 0.5 VEN/SET < 0.5 VEN/SET > 1.4 VEN/SET < 0.5 1.4 0.3 50 -1 500 1 75
s kHz V V s ns s A
Notes: 1. The AAT3132 is guaranteed to meet performance specification over the -40 to 85C operating temperature range and are assured by design, characterization and correlation with statistical process controls.
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High Efficiency 1.5X Fractional Charge Pump for White LED Applications Typical Characteristics
(Unless otherwise noted, VIN = 3.5V, CIN = COUT = C1 = C2 = 1F, TA = 25C) IDIODE vs. VIN (4x20mA)
90 85 80 75 VDIODE = 3.3V VDIODE = 3.4V VDIODE = 3.5V VDIODE = 3.6V 0.850 0.825 0.800 0.775 0.750 0.725 0.700 0.675 0.650 0.625 0.600 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 2.5 3.0 3.5 4.0 4.5 5.0 5.5
AAT3132
VIH and VIL vs. VIN
IDIODE (mA)
70 65 60 55 50 45 40
VIH VIL
VIN (V)
VIN (V)
Turn-On to Full Scale Charge-Pump
ENSET (1V/div) OUT (2V/div) VDIODE (1V/div) IIN (200mA/div) 50s/div
Turn-On to Full Scale Load-Switch
ENSET (1V/div) OUT (2V/div) VDIODE (2V/div) IIN (100mA/div) 50s/div
Turn-Off
VIN
80mA Load Characteristics
ENSET (1V/div) 20mV/div
VDIODE (2V/div) IIN (100mA/div)
OUT
VDIODE 200s/div 1s/div
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High Efficiency 1.5X Fractional Charge Pump for White LED Applications Typical Characteristics
(Unless otherwise noted, VIN = 3.5V, CIN = COUT = C1 = C2 = 1F, TA = 25C) I DIODE vs. Temperature
Output Current Change (%)
2.00% 1.00% 0.00% -1.00% -2.00% -3.00% -4.00% -5.00% -6.00% -7.00% -50 -30 -10 10 30 50 70 90 110
AAT3132
Temperature (C)
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High Efficiency 1.5X Fractional Charge Pump for White LED Applications Functional Block Diagram
VIN
AAT3132
Soft Start Control 1MHz Oscillator Voltage Reference 1.5x Charge Pump
C1+ C1C2+ C2OUT
Current Reference
Quad Output DAC
D1 D2 D3
32x16 bit ROM
EN/SET
S2Cwire Interface
32x16 bit ROM
Single Output DAC
D4
GND
Functional Description
The AAT3132 is a high efficiency (1.5X) fractional charge pump device intended for white LED back light applications. It consists of 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. The AAT3132 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 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, and one (D4) constant current output with a maximum current of 25 or 30mA. The current source output magnitude is controlled by the EN/SET serial data interface. The interface records rising edges of the EN/SET pin, and decodes them into 32 addresses corresponding to individual current level settings.
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High Efficiency 1.5X Fractional Charge Pump for White LED Applications
The 32 addresses are divided up such that outputs D1-D3 can be controlled independently of output D4. For addresses 1 to 8, 9 to 16, 17 to 24, and 25 to 32, outputs D1-D3 start at 0mA and increase from 0.5mA to 20mA in three 8dB steps and three 2.5dB steps. Output D4 remains constant over these address ranges which provides orthogonal control of the two channels. For addresses 1 to 8, D4 is set to 0mA. For addresses 9 to 16, D4 is set to the next brightness setting, and likewise for addresses 17 to 24 and for addresses 25 to 32. This is summarized in Table and Figure 1. The modulo 32 interface wraps states back to state 1 after the 32nd clock. With each EN/SET pulse, the output current changes to the next setting in the address decoding. To change settings to the previous address decoding, 31 EN/SET clock pulses are required. 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 currents 0mA. Additional clocks are required to set the desired current level. 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.
AAT3132
Applications Information
Constant Current Output Level Settings
The constant current source output amplitude for output D1 to D3 and D4 are set via the serial interface according to a logarithmic scale depicted in Figure 1. Using a logarithmic scale, 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 AAT3132 is programmable through its simple serial control (S2CwireTM), 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." Furthermore, with its high speed serial interface (1MHz data rate), the output current of the AAT3132 can 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.
Output Current Level Settings Option 3132
30
25
20
Current (mA)
15
10
5
0 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
Address Code
Figure 1.
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High Efficiency 1.5X Fractional Charge Pump for White LED Applications
Table 1: Constant Current Source Output Programming Levels (mA)
Current Level Settings Address D1-3 D4 (AAT3132) D4(AAT3132-1)
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 0.0 0.5 1.3 3.3 8.3 11.1 15.0 20.0 0.0 0.5 1.3 3.3 8.3 11.1 15.0 20.0 0.0 0.5 1.3 3.3 8.3 11.1 15.0 20.0 0.0 0.5 1.3 3.3 8.3 11.1 15.0 20.0 0 0 0 0 0 0 0 0 1 1 1 1 1 1 1 1 15 15 15 15 15 15 15 15 30 30 30 30 30 30 30 30 0 0 0 0 0 0 0 0 15 15 15 15 15 15 15 15 20 20 20 20 20 20 20 20 25 25 25 25 25 25 25 25
AAT3132
EN/SET Serial Interface (S2CwireTM)
The current source output magnitude is controlled by the EN/SET serial data interface. The interface records rising edges of the EN/SET pin, and decodes them into 32 individual current level settings summarized in Table 1. The modulo 32 interface wraps states back to state 1 after the 32nd clock, so the previous state is achieved by clocking the EN/SET pin 31 times. 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 0. 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.
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High Efficiency 1.5X Fractional Charge Pump for White LED Applications
EN/SET Timing Diagram
tHI tLO tOFF
AAT3132
EN/SET Code
OFF
1
2
3
OFF
LED Selection
The AAT3132 is specifically intended for driving white LEDs. However, the device design will allow the AAT3132 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 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. 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 AAT3132 makes 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.
Power Efficiency and Device Evaluation
The charge pump efficiency discussion in the following sections only account for the efficiency of the charge pump section itself. Due to the unique circuit architecture and design of the AAT3132, it is very difficult to measure efficiency in terms of a percent value comparing input power over output power. Since the AAT3132 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 component count, reliability, operating range and total energy usage...Not just "% efficiency". The AAT3132 efficiency may be quantified under very specific conditions and is dependant upon the input voltage versus the output voltage seen across the loads applied to outputs D1 through D4 for a given constant current setting. The efficiency () can be simply defined as a linear voltage regulator with an effective output voltage that is equal to one and a 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.
Device Switching Noise Performance
The AAT3132 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 AAT3132 soft-start feature prevents noise transient effects associated with in-rush currents during the start up of the charge pump circuit.
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High Efficiency 1.5X Fractional Charge Pump for White LED Applications
POUT PIN 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.
AAT3132
=
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 (%) = 100 VOUT 1.5VIN
Equivalent Series Resistance (ESR)
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.
=
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 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 for measured plots of efficiency versus input voltage and output load current for the given charge pump output voltage options.
Ceramic Capacitor Materials
Ceramic capacitors less than 0.1F are typically made from NPO or COG materials. NPO and COG 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 2.2 F are often available in low cost Y5V and Z5U dielectrics, but capacitors greater than 1F are typically not required for AAT3132 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.
Capacitor Selection
Careful selection of the four external capacitors CIN, C1, C2, COUT is important because they will affect turn on time, output ripple and transient performance. Optimum performance will be obtained when low ESR (<100m) ceramic capacitors are used. In general, low ESR may be defined as less than 100m. A capacitor 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.
Thermal Protection
The AAT3132 has a thermal protection circuit that will shut down the charge pump if the die temperature rises above the thermal limit as is the case during a short circuit of the OUT pin.
Capacitor Characteristics
Ceramic composition capacitors are highly recommended over all other types of capacitors for use with the AAT3132. Ceramic capacitors offer many advantages over their tantalum and aluminum electrolytic counterparts. A ceramic capacitor typically has very
Driving Multiple LEDs, White LED display module back lights and individual LEDs connected in parallel
The AAT3132 D1 to D4 outputs are true constant current sources capable of driving up to 20mA (D1 D3) or 25/30mA (D4) each over the operation input voltage range. Since these outputs are true constant
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High Efficiency 1.5X Fractional Charge Pump for White LED Applications
current sources, they may be connected in parallel to drive a single power output. Any combination of outputs (D1 to D4) may be connected in parallel. The maximum total output current is a sum of how many current sources are parallel connected. This feature is particularly useful to power pre-manufactured display modules which are pre-wired with white LED backlights connected in a parallel circuit configuration. Any combination of outputs may be connected in parallel to drive groups of LEDs. The AAT3132 internal current source reference circuit bases feedback from current sensed on the D1 and D4 outputs. For best operation, the only requirement for this type of application is the outputs D1 and D4 should always be connected to the load circuit. The AAT3132 may be used to drive multiple LEDs having differing forward voltages. Using feedback techniques, the current in D1 to D3 are referenced to the current in the LED connected to D1. Current source output D4 is its own reference. If all LEDs are of similar type, the diodes will be matched in current, maintaining uniform LED brightness despite variations in manufacturer, production, etc. If however, the diodes are dramatically different in type comprising a mix of high-VF type and low-VFtype LEDs, the AAT3132 has the capability to optimally drive up to four LEDs of one-type and up to two LEDs of another type simultaneously. Such a feature can be useful for driving different color LEDs; driving both display backlight and photoflash LEDs; or for driving main-LCD and sub-LCD display LED backlights from a single Charge Pump IC. For example, when driving independent RGB LEDs, the green and blue type LEDs typically require a high VF to operate (e.g. 3.7V) while the red LED needs a low forward voltage (e.g. 2V). By connecting the green and blue diodes to outputs D1 to D3 and the red diodes to D4, good control and uniformity in brightness is maintained despite the 2V difference in the diode forward voltages. Similarly, if a 4V photo-flash LED-array is connected to outputs D1 through D3 (with the outputs shorted together) and two 3.3V sub-LCD-display backlight LEDs are connected to output D4, then the AAT3132 can optimally drive each set of LEDs at the programmed current level (see application schematics).
AAT3132
Additional Application Circuit
VIN C1+ C1 1F VOUT VBATTERY CIN 1F COUT 1F C1C2+ C2 1F D1 D2
AAT3132
C2D1 D2 D3
D3
D4
EN/SET
EN/SET GND
D4 D5 D6
AAT3132 Driving Two Groups of Paralleled White LEDs (e.g. main-LCD & sub-LCD backlights)
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High Efficiency 1.5X Fractional Charge Pump for White LED Applications Ordering Information
Package TSOPJW-12 TSOPJW-12 Marking1 JAXYY Part Number (Tape and Reel) AAT3132ITP-T1 AAT3132ITP-1-T1
AAT3132
Note: Sample stock is generally held on all part numbers listed in BOLD. Note 1: XYY = assembly and date code.
Package Information
TSOPJW-12
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
0.055 0.045
4 4
0.010
0.15 0.05
0.45 0.15 2.75 0.25
All dimensions in millimeters.
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High Efficiency 1.5X Fractional Charge Pump for White LED Applications
AAT3132
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, and advise customers 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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