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High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications General Description
The AAT3134 is a low noise, constant frequency charge pump DC/DC converter that uses a dual mode Load Switch (1X) and fractional (1.5X) conversion to maximize efficiency for White LED applications. The device can be used to produce current levels up to 20mA in each of its six outputs to drive LED's from a 2.7V to 5.5V input. Outputs may be operated individually or paralleled for driving higher-current LED's. Low external parts counts (two 1F flying capacitors and two small 1F capacitors at VIN, and OUT) make the AAT3134 ideally suited for small battery-powered applications. AnalogicTech's Simple Serial Control (S2CwireTM) interface is used to enable, disable and set the LED drive current in two groups of four outputs and two outputs with multiple level independently controlled brightness scales. The AAT3134 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 AAT3134 is available in a 16-pin quad QFN package.
AAT3134
Features
* * * * * * * * * * * * * * *
ChargePumpTM
VIN Range: 2.7 - 5.5 Volts < 1.0A of Shutdown 1 MHz Switching Frequency Fully Independent Display Lighting Dual Mode 1x and 1.5x Charge Pump for Maximum Efficiency Drives Low-VF & High-VF Type LED's Up to Six 20mA Outputs Multi Position Brightness Scale with Digital Control Low Noise Constant Frequency Operation Small Application Circuit Regulated Output Current Automatic Soft-Start No Inductors 16-pin QFN package -40 to +85C Temperature range
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
AAT3134
C2D1 D2 D3 D4 D5 D6
EN/SET
EN/SET GND
D4
D3
D2
D1
D6
D5
Sub Display
Main Display
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High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications Pin Descriptions
Pin #
1 2 3 4 5 6 7 8,13 9 10 11 12 14 15 16
AAT3134
Symbol
D2 D5 D6 D3 D4 C1+ C1NC OUT C2+ C2GND IN EN/SET D1
Function
Current source output #2 Current source output #5 Current source output #6 Current source output #3 Current source output #4 Flying Capacitor 1 + terminal. Connect a 1F capacitor between C1+ and C1-. Flying Capacitor 1 - terminal No Connection Charge pump output. Requires 1F capacitor connected between this pin and ground. Flying Capacitor 2 + terminal. Connect a 1F capacitor between C2+ and C2-. Flying Capacitor 2 - terminal Ground Input power supply. Requires 1F capacitor connected between this pin and ground. Control Pin Current source output #1
Pin Configuration
QFN44-16 (top view)
EN/SET
15
NC IN
14 13
D1
16
D2 D5 D6 D3
1
12
GND C2C2+ OUT
2
11
3
10
4 5 6 7 8
9
C1+ D4
NC C1-
2
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High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications Absolute Maximum Ratings1
Symbol
VIN VOUT FB,VEN/SET VEN/SET(MAX) IOUT 2 TJ
AAT3134
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 -0.3 to 6.0 -0.3 to 6.0 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 JC PD
Description
Thermal Resistance1 Thermal Resistance1 Maximum Power Dissipation1
Value
50 15 2
Units
C/W W
Note 1: Mounted on a FR4 board.
Electrical Characteristics1
VIN = 3.5V, CIN = COUT = C1 = C2 = 1.0F; TA = -40 to 85 C. Unless otherwise noted, typical values are TA = 25C. Symbol Description Conditions Min
2.7 3.0 VIN 5.5, Active, No Load Current EN/SET=0 VIN = 3.6, Code = 32 VD1:D4 = 3.6, VIN = 3.5V VD5:VD6 = 3.6, VIN = 3.5V 1.8
Typ
Max
5.5 3.5 1.0 22
Units
V mA A mA % s kHz %
Input Power Supply VIN Operation Range Operating Current ICC Shutdown Current IDX(MAX) Maximum Output Current I(D-Match) Current Matching between any two outputs Charge Pump Section TSS Soft start time FCLK Clock Frequency Charge Pump Section Efficiency CP EN/SET VEN(L) VEN(H) TEN/SET LO TEN/SET HI TOFF Input Current ISHDN
18
20 0.5 0.5 200 1000 93
VIN = 3.5V, IOUT(TOTAL) = 120mA, Measured from IN to OUT
Enable Threshold Low Enable Threshold High EN/SET low time Minimum EN/SET high time EN/SET Off Timeout EN/SET input leakage
0.5 VEN/SET < 0.5 VEN/SET > 1.4 VEN/SET < 0.5 1.4 0.3 50 -1.0 500 1.0 75
V V s ns s A
Note 1: The AAT3134 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 1X/1.5X Fractional Charge Pump for White LED Applications Typical Characteristics
(Unless otherwise noted, VIN = 3.5V, CIN = COUT = C1 = C2 = 1F, TA = 25C) Efficiency vs. VIN (4x20mA)
100% 95% 90% VDIODE = 3.3V VDIODE = 3.4V 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 VDIODE = 3.5V VDIODE = 3.6V 90 85 80 75
AAT3134
IDIODE vs. VIN (4x20mA)
VDIODE = 3.3V VDIODE = 3.4V VDIODE = 3.5V VDIODE = 3.6V
Efficiency
IDIODE (mA)
70 65 60 55 50 45 40 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
VIN (V)
VIN (V)
Quiescent Current vs. VIN
2.4 2.2 2.0 1.8 1.6 1.4 1.2 1.0 0.8 0.6 0.4 0.2 0.0 2.50 0.850 0.825 0.800 0.775 VDIODE = 3.3V VDIODE = 3.4V VDIODE = 3.5V VDIODE = 3.6V 0.750 0.725 0.700 0.675 0.650 0.625 0.600 3.00 3.50 4.00 4.50 5.00 5.50 2.5 3.0
VIH and VIL vs. VIN
Quiescent Current (mA)
VIH VIL
3.5
4.0
4.5
5.0
5.5
VIN (V)
VIN (V)
4
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High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications Typical Characteristics
(Unless otherwise noted, VIN = 3.5V, CIN = COUT = C1 = C2 = 1F, TA = 25C) Turn-On to Full Scale Charge-Pump
ENSET (1V/div) OUT (2V/div) VDIODE (1V/div) IIN (200mA/div) 50s/div
AAT3134
Turn-On to Full Scale Load-Switch
ENSET (1V/div) OUT (2V/div) VDIODE (2V/div) IIN (100mA/div) 50s/div
Charge Pump to Load Switch (80mA)
VIN (10mV/div) OUT (2V/div) VDIODE (2V/div) IIN (100mA/div) 50s/div
Load Switch to Charge Pump (80mA)
VIN (20mV/div) OUT (1V/div) VDIODE (1V/div) IIN (200mV/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 1X/1.5X Fractional Charge Pump for White LED Applications Functional Block Diagram
VIN
AAT3134
Soft Start Control
C1+ C11x/1.5x Charge Pump
1MHz Oscillator
C2+ C2OUT
Voltage Reference
D1
Current Reference Quad Output DAC
D2 D3 D4
32x16 bit ROM
EN/SET
S2CWire Interface
32x16 bit ROM
Dual Output DAC
D5 D6
GND
Functional Description
The AAT3134 is a dual mode Load Switch (1X) and high efficiency (1.5X) fractional charge pump device intended for white LED back light 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. This function significantly enhances over all device efficiency when the input voltage level is greater then the voltage required at the constant current source outputs. The 1X Load Switch/1.5X charge pump mode decision is based on the voltage levels sensed on either the D1 output or the D5 output, which ever is greater. Switchover between the 1.5X (chargepump) operating mode and the 1X (load switch) 6
mode occurs automatically (as a function of input and output voltages) and does not require user intervention to maintain maximum efficiency. The AAT3134 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 four (D1 to D4) constant current outputs to drive four individual LED's with a maximum current of 20mA each, and two (D5 and D6) constant current outputs with a maximum current of 20mA. 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. The 32 addresses are divided up such that outputs D1-D4 can be controlled independently of outputs D5-D6. For addresses 1 to 6, 7 to 12, 13 to 18, 19 to 24, and 25 to 30, outputs D1-D4 start at 0mA and increase from 1mA to 20mA in four steps. Outputs D5 and D6 remain
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High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications
constant over these address ranges which provides orthogonal control of the two channels. For addresses 1 to 6, D5 and D6 are set to 0mA, addresses 7 to 12 are 1mA, addresses 13 to 18 are 10mA, addresses 19 to 24 are 12mA, and addresses 25 to 30 are 15mA. For maximum brightness control, addresses 31 and 32 set D5 and D6 to the maximum 20mA level. For design flexibility, D1-D4 are set to 0mA at address 31, and 20mA at address 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.
AAT3134
Applications Information
Constant Current Output Level Settings
The constant current source output amplitude for output D1 to D4 and D5 to D6 are set via the serial interface according to the scale described in figure 1 and the previous section. Because the outputs D1 to D6 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 AAT3134 is programmable through the S2CWire 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." Furthermore, with its high speed serial interface (1MHz data rate), the output current of the AAT3134 can be changed successively to brighten or dim LED's, 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
20 18 16
Current (mA)
14 12 10 8 6 4 2 0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Address Code
Figure 1.
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
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High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications
Table 1: Constant Current Source Output Programming Levels (mA)
Address
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
AAT3134
EN/SET Serial Interface (S2CwireTM)
The current source output magnitude is controlled by the EN/SET serial 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.
Current Level Settings D1-D4 D5-D6
0 1 10 12 15 20 0 1 10 12 15 20 0 1 10 12 15 20 0 1 10 12 15 20 0 1 10 12 15 20 0 20 0 0 0 0 0 0 1 1 1 1 1 1 10 10 10 10 10 10 12 12 12 12 12 12 15 15 15 15 15 15 20 20
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High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications
EN/SET Timing Diagram
tHI tLO tOFF
AAT3134
EN/SET Code
OFF
1
2
3
OFF
LED Selection
The AAT3134 is specifically intended for driving white LED's. However, the device design will allow the AAT3134 to drive most types of LED's 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) LED's, infrared (IR) diodes for remotes, and other loads benefiting from a controlled output-current generated from a varying input-voltage. Since the D1 to D6 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 LED's. The low-dropout current-sources in the AAT3134 makes it capable of driving LED's 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 LED's without complication
ically ten times less than inductor-based DC/DC boost converter white LED backlight solutions. The AAT3134 soft-start feature prevents noise transient effects associated with in-rush currents during the start up of the charge pump circuit..
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 AAT3134, it is very difficult to measure efficiency in terms of a percent value comparing input power over output power. Since the AAT3134 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."
Device Switching Noise Performance
The AAT3134 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, typ-
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High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications
The AAT3134 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. Depending upon the case of VIN being greater than the specific voltage seen across the load on D1 (or D4) the device will operate in "Load Switch" mode. If VIN is less than the voltage required on the constant current source, 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 for each operational mode lator 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. POUT PIN
AAT3134
=
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
Load Switch Mode Efficiency
The AAT3134 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 then 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-
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.
Capacitor Selection
(%) = 100 VOUT VIN 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.
Charge Pump Section Efficiency
The AAT3134 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 regu-
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High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications
Capacitor Characteristics
Ceramic composition capacitors are highly recommended over all other types of capacitors for use with the AAT3134. 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.
AAT3134
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 2.2F are often available in low cost Y5V and Z5U dielectrics, but capacitors greater than 1F are typically not required for AAT3134 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
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.
Thermal Protection
The AAT3134 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.
Additional Application Circuits
VIN C1+ C1 1F VOUT VBATTERY CIN 1F C OUT 1F C1C2+ C2 1F
RB* RB* R B* RB*
D1
D2
D3
D4
AAT3134
C2D1 D2 D3 D4 D5 D6
Resistor R is optional
EN/SET
EN/SET GND
D5
D6
R
R
Resistor R is optional
*In some applications, white LED forward voltages (VF) 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: RB = VSOURCE - VF IF
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High Efficiency 1X/1.5X Fractional Charge Pump for White LED Applications Ordering Information
Package QFN44-16 Marking1 JBXYY Part Number (Tape and Reel) AAT3134ISN-T1
AAT3134
Note 1: XYY = Assembly and date code.
Package Information
QFN44-16
0.600 0.050
Pin 1 Dot By Marking
0.330 0.050
13 16
Pin 1 Identification
0.650 BSC
1
4.000 0.050
R0.030Max
9 4
8
5
4.000 0.050
2.280 REF
Top View
Bottom View
2.400 0.050
0.0125 0.0125
0.203 0.025
Side View
All dimensions in millimeters.
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 12
3134.2004.04.1.0
0.900 0.050
0.450 0.050

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