A1425 Datasheet

A1425
High Accuracy Analog Speed Sensor IC with Integrated Filter
Capacitor and Dual Zero-Crossing Output Signal
Features and Benefits
Description
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The A1425 AC-coupled Hall-effect sensor IC is a monolithic
integrated circuit that switches in response to changing
differential magnetic fields created by rotating ring magnets
and, when coupled with a magnet, by ferrous targets. The device
is a true zero-crossing detector: the output switches precisely
when the difference in magnetic field strength between the
two Hall elements is zero. A unique dual-comparator scheme
provides for accurate switching at the zero crossing on both the
positive and negative-going regions of the differential signal,
while utilizing hysteresis to prevent false switching. The zerocrossing nature of this device provides excellent repeatability
and accuracy for crankshaft applications.
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Used in sensing motion of ring magnet or ferrous targets
Integrated filter capacitor
Wide operating temperature range
Operation with magnetic input signal frequency from
20 Hz to 20 kHz
Resistant to EMI
Large effective air gaps
4.0 to 26.5 V supply operating range
Output compatible with both TTL and CMOS logic
families
Reverse battery protection
Resistant to mechanical and thermal stress
Accurate true zero-crossing switchpoint
Package: 4 pin SIP (suffix K)
Changes in field strength at the device face, which are
induced by a moving target, are sensed by the two integrated
Hall transducers. The transducers generate signals that are
differentially amplified by on-chip electronics. This differential
design provides immunity to radial vibration within the
operating air gap range of the A1425, by rejection of the
common mode signal. Steady-state magnet and system offsets
are eliminated using an on-chip differential band-pass filter.
This filter also provides relative immunity to interference from
electromagnetic sources.
Continued on the next page…
Functional Block Diagram
VS+
VCC
(Pin 1)
Diagnostic
Circuitry
Regulator
Bandpass Filter Integrated
Tracking Capacitor
Dual Hall
Transducers
VOUT
(Pin 2)
Comparator
0.1 uF
Hall
Amp
Gain
Stage
VREF
GND
(Pin 4)
1425-DSa, Rev.3
TEST
(Pin 3)
(Required)
High Accuracy Analog Speed Sensor IC with Integrated
Filter Capacitor and Dual Zero-Crossing Output Signal
A1425
Description (continued)
The device utilizes advanced temperature compensation for the
high-pass filter, sensitivity, and Schmitt trigger switchpoints,
to guarantee optimal operation to low frequencies over a wide
range of air gaps and temperatures.
Each Hall effect digital integrated circuit includes a voltage
regulator, two Hall effect elements, temperature compensating
circuitry, a low-level amplifier, band-pass filter, Schmitt trigger,
and an output driver, which requires a pull-up resistor. The onboard regulator permits operation with supply voltages from 4.0
to 26.5 V. The output stage can easily switch 20 mA over the full
frequency response range of the device, and is compatible with
both TTL and CMOS logic circuits.
The device is packaged in a 4-pin plastic SIP. It is lead (Pb) free,
with 100% matte tin plated leadframe.
Selection Guide
A1425LK-T
*Contact Allegro
Switchpoints
BOP(MAX)
BRP(MIN)
(G)
(G)
Packing*
Part Number
–11
Bulk, 500 pieces/bag
11
for additional packing options.
Absolute Maximum Ratings
Characteristic
Symbol
Supply Voltage
VCC
Reverse Supply Voltage
VRCC
Notes
Refer to Power Derating section
Rating
Units
28
V
–18
V
Continuous Output Current
IOUT
25
mA
Continuous Reverse-Output Current
IROUT
–50
mA
–40 to 150
ºC
Operating Ambient Temperature
Maximum Junction
Storage Temperature
Pin-out Diagram
1
2
3
TA
Range L
TJ(max)
165
ºC
Tstg
–65 to 170
ºC
Terminal List Table
Name
Number
VCC
1
VOUT
2
TEST
3
GND
4
4
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
2
A1425
High Accuracy Analog Speed Sensor IC with Integrated
Filter Capacitor and Dual Zero-Crossing Output Signal
OPERATING CHARACTERISTICS Valid at TA = – 40ºC to 150ºC, TJ ≤ 165°C; over operational air gap range and VCC within
operating range, unless otherwise noted. Typical operating parameters: VCC = 12 V and TA = 25°C.
Characteristic
Symbol
Test Conditions
Min.
Typ.
Max.
Units
4.0
–
26.5
V
–
4.2
7.0
mA
–
140
400
mV
–
–
5
μA
VCC = –18 V
–
–
–1
mA
ELECTRICAL CHARACTERISTICS
Supply Voltage
VCC
Supply Current
ICC
Output Saturation Voltage
Output Leakage Current
Operating; TJ < TJ(max)
VOUT(SAT) ISINK = 20 mA
IOFF
VOUT = 24 V, Bdiff = 0
PROTECTION COMPONENT CHARACTERISTICS
Reverse Supply Current
IRCC
Supply Zener Current
IZSupply
VS = 28 V
–
–
10
mA
Supply Zener Clamp Voltage1
VZSupply
ICC = 10 mA, TA = 25°C
28
33
37
V
Output Zener Current
IZOutput
VOUT = 28 V
–
–
3
mA
Output Zener Clamp Voltage
VZOutput
IOUT = 3 mA, TA = 25°C
28
–
–
V
Output Short Circuit Current Limit2
IOUTS(lim)
–
–
50
mA
t < tResponse
–
High
–
V
tPO
VCC > VCC(min)
–
4.5
9
ms
tSettle
fBdiff ≥ 100 Hz
0
–
50
ms
RESPONSE CHARACTERISTICS
Power-On State
Power-On Time3,7
Settling Time4,7
Response
Time7
POS
4.5
–
59
ms
Upper Corner Frequency
tResponse Equal to tPO + tS; fBdiff ≥ 100 Hz
fcu
–3 dB, single pole
20
–
–
kHz
Lower Corner Frequency
fcl
–3 dB, single pole
–
–
20
Hz
Output Rise Time5
tr
RPU = 1 kΩ, COUT2 = 10 pF
–
–
200
ns
Output Fall Time
tf
RPU = 1 kΩ, ISINK = 20 mA, COUT2 = 10 pF
–
–
200
ns
–11
0
11
G
–11
0
11
G
50
–
1250
G
OUTPUT CHARACTERISTICS
MAGNETIC CHARACTERISTICS
Output Off Switchpoint6,7
BOP
Output On Switchpoint6,7
BRP
Applied Magnetic Field7,8
Bdiff
Bdiff increasing, fBdiff = 200 Hz, Bdiff = 50 Gp-p;
digital output signal switches low to high
Bdiff decreasing, fBdiff = 200 Hz, Bdiff = 50 Gp-p;
digital output signal switches high to low
Differential p-p magnetic field
1I
CC equivalent to ICC(max) + 3 mA.
2I
OUT does not change state when IOUT > IOUTS(lim) , regardless of changes in the impinging magnetic field.
3Time required to initialize device.
4Time required for the output switchpoints to be within specification.
5Output Rise Time will be dominated by the RC time constant.
6For other sinusoidal signal frequencies and magnetic fields, –B
OP = BRP = sinα(Bdiff ⁄ 2) ± 25%, where α is the phase shift shown in the Characteristic
Data section.
7See Definitions of Terms section.
8Exceeding the maximum magnetic field may result in compromised absolute accuracy.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
3
High Accuracy Analog Speed Sensor IC with Integrated
Filter Capacitor and Dual Zero-Crossing Output Signal
A1425
THERMAL CHARACTERISTICS may require derating at maximum conditions, see application information
Characteristic
Symbol
Test Conditions
RθJA
Package Thermal Resistance
Single-layer PCB, with copper limited to solder pads
177
ºC/W
Maximum Power Dissipation, PD(max)
Power Derating Curve
30
900
28
850
VCC(max)
26
800
750
24
700
22
650
20
18
16
(RθJA = 177 ºC/W)
14
12
10
8
6
VCC(min)
4
2
Power Dissipation, PD (m W)
Maximum Allowable VCC (V)
Rating Units
600
(R
θJ
550
A
500
450
400
=
17
7
ºC
/W
)
350
300
250
200
150
100
50
0
0
20
40
60
80
100
120
140
160
180
Temperature (ºC)
20
40
60
80
100
120
140
160
180
Temperature (°C)
Definitions of Terms
The following provide additional information about some of
the parameters cited in the Operating Characteristics table.
For additional information, visit the Allegro Web site at
www.allegromicro.com.
Applied Magnetic Field, Bdiff – The differential magnetic flux
density which is calculated as the arithmetic difference of the
flux densities observed by each of the two Hall elements.
Output Off Switchpoint (Operate Point), BOP – The value of
increasing differential magnetic flux density at which the device
output switches from low to high. This value may be greater than
or less than 0 G.
Output On Switchpoint (Release Point), BRP – The value of
decreasing differential magnetic flux density at which the device
output switches from high to low. This value may be greater
than or less than 0 G.
Power-On Time, tPO – The time needed by the device, after
power is applied, to initialize all circuitry necessary for proper
operation.
Settling Time, tSettle – The time required by the device, after tPO,
and after a valid magnetic signal has been applied, to provide
proper output transitions. Settling time is a function of magnetic
offset, offset polarity, signal phase, signal frequency, and signal
amplitude.
Response Time tResponse – The total time required for generating zero-crossing output transitions after power-up (the sum of
power-on time and settling time).
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
4
High Accuracy Analog Speed Sensor IC with Integrated
Filter Capacitor and Dual Zero-Crossing Output Signal
A1425
Empirical Results
Output Voltage by Ambient Temperature
Supply Current by Ambient Temperature
7
VCC (V)
6
ICC (mA)
5
VOUT(SAT) (mV)
4.5
12
12.0
26
20.0
4
3
2
1
0
–50
0
50
100
150
200
500
450
400
350
300
250
200
150
100
50
0
–50
ISINK = 20 mA
VCC (V)
4.5
12.0
20.0
0
Supply Current by Supply Voltage
TA (ºC)
6
ICC (mA)
5
VOUT(SAT) (mV)
150
25
–40
4
3
2
1
0
20
VCC (V)
150
200
Output Voltage by Supply Voltage
7
10
100
TA (ºC)
TA (ºC)
0
50
30
500
450
400
350
300
250
200
150
100
50
0
0
ISINK = 20 mA
TA (ºC)
150
25
–40
5
10
15
20
25
VCC (V)
Continued on next page.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
5
High Accuracy Analog Speed Sensor IC with Integrated
Filter Capacitor and Dual Zero-Crossing Output Signal
A1425
Empirical Results, continued
Repeatability (º of Rotation)
116
Air Gap (mm)
Repeatability (º of Rotation)
116
Air Gap (mm)
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
6
High Accuracy Analog Speed Sensor IC with Integrated
Filter Capacitor and Dual Zero-Crossing Output Signal
A1425
Simulation Results
A1425 Minimum Switching Fields
Over the Range of Ambient Operating Temperatures, TA
fBdiff(low) = 15 Hz, fBdiff(high) ≈ 30 kHz
40
35
30
25
Bdiff(min) (G)
25
150
20
–40
15
10
5
0
0.01
0.1
1
10
40
Frequency, fBdiff (kHz)
A1425 Typical Phase Shift
Over the Range of Applied Magnetic Fields, Bdiff
fBdiff(low) = 15 Hz, fBdiff(high) = 30 kHz
40
30
50
100
500
10 750
Phase Shift (º)
20
0
–10
1250
Bdiff in Gp-p
–20
–30
–40
–50
–60
0.01
0.1
Frequency, fBdiff
1
(kHz)
10
40
Continued on next page.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
7
High Accuracy Analog Speed Sensor IC with Integrated
Filter Capacitor and Dual Zero-Crossing Output Signal
A1425
Simulation Results, continued
A1425 Typical Delay
Over the Range of Applied Magnetic Fields, Bdiff
fBdiff(low) = 15 Hz, fBdiff(high) = 30 kHz
15
10
Bdiff in Gp-p
IOUT Lagging
0
12
–5
–10
50
75
0
5
50
0
50
100
IOUT Delay (μs)
IOUT Leading
20
–15
–20
0.1
1
Frequency, fBdiff (kHz)
40
10
Positive values of delay indicate a lagging output, while negative values indicate a leading output.
IOUT Delay (μs)
IOUT Leading
A1425 Typical Delay
Over the Range of Applied Magnetic Fields, Bdiff
fBdiff(low) = 15 Hz, fBdiff(high) = 30 kHz
1000
0
–1000
1250
750
500
–2000
IOUT Lagging
–3000
–4000
–5000
Bdiff in Gp-p
0
10
50
–6000
0
100
Frequency, fBdiff (Hz)
Positive values of delay indicate a lagging output, while negative values indicate a leading output.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
8
A1425
High Accuracy Analog Speed Sensor IC with Integrated
Filter Capacitor and Dual Zero-Crossing Output Signal
Device Evaluation: EMC Characterization
Please contact Allegro MicroSystems for EMC performance information.
Test Name
Reference Specification
ESD – Human Body Model*
AEC-Q100-002
ESD – Machine Model*
AEC-Q100-003
Conducted Transients
ISO 7637-1
Direct RF Injection
ISO 11452-7
Bulk Current Injection
ISO 11452-4
TEM Cell
ISO 11452-3
*ESD testing is performed with no external components.
Vs
R1
RPU
1
VCC
C1
A1425
4
GND
VOUT
2
TEST
COUT2
3
(Required)
Recommended EMC test circuit.
Component
RPUa
R1b
C1
COUTc
Value
1.2
100
0.1
4.7
Units
kΩ
Ω
μF
nF
aPull-up resistor not required for protection but for normal operation.
bFor improved CI performance
cFor improved BCI performance
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
9
High Accuracy Analog Speed Sensor IC with Integrated
Filter Capacitor and Dual Zero-Crossing Output Signal
A1425
Functional Description
The A1425 is a versatile high-precision differential Hall-effect
device that can be used in a wide range of applications. Proper
choice of the target material and shape, and assembly techniques
enables large working air gaps and high switchpoint accuracy
over the device operating temperature range.
Start-up
During power-on time, tPO, the output signal, VOUT, is high.
Beyond this time, if the applied magnetic field, Bdiff, is absent or
less than 50 G peak-to-peak, the switching state and VOUT polarity are indeterminate. VOUT will be valid for Bdiff > 50 Gp-p, after
the additional settling time, tSettle, has also elapsed. Also during
tPO, a circuit in the A1425 is briefly enabled that charges the onchip capacitor. This feature reduces tPO, relative to the long RC
time constant of a high-pass filter.
Device Operation
The A1425 sensor IC contains two integrated Hall transducers
that are used to differentially respond to a magnetic field across
the surface of the IC. Referring to figure 1, the trigger switches
the output off (output high) when the differential magnetic field
crosses zero while increasing in strength (referred to as the positive direction), and switches the output on (output low) when
the differential magnetic field crosses zero while decreasing (the
negative direction).
Delay
The on-chip band-pass filter induces delay in the output signal,
VOUT, relative to the applied magnetic field, Bdiff. Simulation data
shown in the Characteristic Data section quantify the effect of the
input signal amplitude on the phase shift of the output.
The operation is achieved through the use of two separate comparators. Both comparators use the same reference point, 0 G, to
provide high accuracy, but one comparator has a positive hysteresis, BHYS1, and the other a negative hysteresis, BHYS2. Therefore,
one comparator switches (BOP) at the zero crossing on an increasing differential signal and the other switches (BRP) at the zero
crossing on a decreasing differential signal. The hysteresis on
each comparator precludes false switching on noise or target jitter.
AC-Coupled Operation
Steady-state magnet and system offsets are eliminated using an
on-chip differential band-pass filter. The low and high frequency
poles of this band-pass filter are set using internal integrated
capacitors and resistors. The differential structure of this filter
improves the ability of the IC to reject single-ended noise on
the ground (GND pin) or supply line (VCC pin) and, as a result,
makes it more resistant to electromagnetic interference typically
seen in hostile remote-sensing environments.
11.0
Applied Magnetic
Field, Bdiff
BOP(typ)
0.0

–11.0
BOP(max) / BRP(max)
BHYS1 
BRP(typ)
BHYS2
BOP(min) / BRP(min)
Comparator 1
Comparator 2
Switching State
Output Signal, VOUT
Off
On
Off
t+
Figure 1. Typical output characteristics with dual comparator operation. Characteristics shown without delay, see Characteristic
Data section charts for delay and phase shift contributions.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
10
A1425
High Accuracy Analog Speed Sensor IC with Integrated
Filter Capacitor and Dual Zero-Crossing Output Signal
Applications Information
Target Selection
Power Supply Protection
The zero-crossing switchpoints and AC-coupled operation of this
device make target selection important. For high-density target
geometries or small target features that produce a sinusoidal
magnetic signal, the high-pass filter is capable of filtering offsets
that may be induced in the final device output. If such offset is
present, and the target has larger features, then the high-pass
filter may not be effective at higher speeds and an accuracy shift
may occur. These relationships are shown in figure 2.
The A1425 contains an on-chip voltage regulator and can operate over a wide supply voltage range. In applications that operate
the device from an unregulated power supply, transient protection must be added externally. For applications using a regulated
line, EMI/RFI protection may still be required. The circuit
shown in figure 3 is the most basic configuration required for
proper device operation.
Differential Magnetic
Flux Density, Bdiff
Large Feature (Tooth)
Valley
+B
(a)
0
VCC
1
–B
Device Output
Voltage, VOUT
+V
Differential Magnetic
Flux Density, Bdiff
RPU
0.1 uF
4
A1425
2
VOUT
3
(Required)
0
+B
t
Figure 3. Basic application circuit. A pull-up resistor, RPU, is required
with the output driver.
Output Edge
Shift
(b)
0
–B
Device Output
Voltage, VOUT
+V
0
t
Figure 2. Large Feature Effects. (a) Large target feature but no device offset,
normal edge position. (b) Large target feature with negative device offset, shifted
(advanced) output edge position.
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
11
High Accuracy Analog Speed Sensor IC with Integrated
Filter Capacitor and Dual Zero-Crossing Output Signal
A1425
Power Derating
The device must be operated below the maximum junction
temperature of the device, TJ(max). Under certain combinations of peak conditions, reliable operation may require derating
supplied power or improving the heat dissipation properties of
the application. This section presents a procedure for correlating
factors affecting operating TJ. (Thermal data is also available on
the Allegro MicroSystems Web site.)
The Package Thermal Resistance, RJA, is a figure of merit summarizing the ability of the application and the device to dissipate
heat from the junction (die), through all paths to the ambient air.
Its primary component is the Effective Thermal Conductivity,
K, of the printed circuit board, including adjacent devices and
traces. Radiation from the die through the device case, RJC, is
relatively small component of RJA. Ambient air temperature,
TA, and air motion are significant external factors, damped by
overmolding.
The effect of varying power levels (Power Dissipation, PD), can
be estimated. The following formulas represent the fundamental
relationships used to estimate TJ, at PD.
PD = VIN × IIN

T = PD × RJA
TJ = TA + ΔT
Reliability for VCC at TA = 150°C, using minimum-K PCB
Observe the worst-case ratings for the device, specifically:
RJA = 177°C/W, TJ(max) = 165°C, VCC(max) = 26.5 V, and
ICC(max) = 7.0 mA.
Calculate the maximum allowable power level, PD(max). First,
invert equation 3:
Tmax = TJ(max) – TA = 165 °C – 150 °C = 15 °C
This provides the allowable increase to TJ resulting from internal
power dissipation. Then, invert equation 2:
PD(max) = Tmax ÷ RJA = 15°C ÷ 177 °C/W = 84 mW
Finally, invert equation 1 with respect to voltage:
VCC(est) = PD(max) ÷ ICC(max) = 84 mW ÷ 7.0 mA = 12 V
(2)
The result indicates that, at TA, the application and device can
dissipate adequate amounts of heat at voltages ≤VCC(est).
(3)
PD = VCC × ICC = 5.0 V × 4.2 mA = 21.0 mW
T = PD × RJA = 21.0 mW × 177 °C/W = 3.7°C
TJ = TA + T = 25°C + 3.7°C = 28.7°C
Example
(1)
For example, given common conditions such as: TA= 25°C,
VCC = 5.0 V, ICC = 4.2 mA, and RJA = 177 °C/W, then:

A worst-case estimate, PD(max), represents the maximum allowable power level (VCC(max), ICC(max)), without exceeding
TJ(max), at a selected RJA and TA.
Compare VCC(est) to VCC(max). If VCC(est) ≤ VCC(max), then reliable operation between VCC(est) and VCC(max) requires enhanced
RJA. If VCC(est) ≥ VCC(max), then operation between VCC(est)
and VCC(max) is reliable under these conditions.
For example, when a standard diode with a 0.7 V drop is used:
VS(max) = 12 V + 0.7 V = 12.7 V
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
12
High Accuracy Analog Speed Sensor IC with Integrated
Filter Capacitor and Dual Zero-Crossing Output Signal
A1425
Package K, 4-pin SIP
+0.08
5.21 –0.05
45°
B
E
2.20
E
1.55 ±0.05
1.50
D
NNNN
1.29 E
+0.08
3.43 –0.05
E1
E2
2.16
MAX
Mold Ejector
Pin Indent
Branded
Face
2
3
D Standard Branding Reference View
0.84 REF
N = Device part number
Y = Last two digits of year of manufacture
W = Week of manufacture
For Reference Only; not for tooling use (reference DWG-9010)
Dimensions in millimeters
Dimensions exclusive of mold flash, gate burrs, and dambar protrusions
Exact case and lead configuration at supplier discretion within limits shown
4
14.73 ±0.51
+0.06
0.38 –0.03
+0.07
0.41 –0.05
1
45°
A
1
YYWW
A
Dambar removal protrusion (8X)
B
Gate and tie bar burr area
C
Branding scale and appearance at supplier discretion
D Active Area Depth, .0.42 mm
E Hall elements (E1 and E2); not to scale
1.27 NOM
Copyright ©2005-2013, Allegro MicroSystems, LLC
Allegro MicroSystems, LLC reserves the right to make, from time to time, such departures from the detail specifications as may be required to
permit improvements in the performance, reliability, or manufacturability of its products. Before placing an order, the user is cautioned to verify that
the information being relied upon is current.
Allegro’s products are not to be used in life support devices or systems, if a failure of an Allegro product can reasonably be expected to cause the
failure of that life support device or system, or to affect the safety or effectiveness of that device or system.
The information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, LLC assumes no responsibility for its
use; nor for any infringement of patents or other rights of third parties which may result from its use.
For the latest version of this document, visit our website:
www.allegromicro.com
Allegro MicroSystems, LLC
115 Northeast Cutoff
Worcester, Massachusetts 01615-0036 U.S.A.
1.508.853.5000; www.allegromicro.com
13
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