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Datasheet: MLX90125 (Melexis, Inc.)

Antenna Coil For MLX90109

 

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3901090125
Page 1 of 7
Aug/02
Rev.001
Features and Benefits
Matches standard capacitance values for realizing resonance
Tight tolerances: inductance value down to +/-3%
Optimized for Read and/or Write performance with the MLX90109
Optimized for minimum area coverage on PCB
Long leads for flexible mounting in modules
Lightweight
Cost optimized
Applications
Lightweight Portable readers, readers with multiple antenna's ...

Ordering Information
Part No.
Temperature Suffix
Package Code
Options(Internal diameter, Inductance)
MLX90125
C (0C to 70C)
ZA
A (17mm ID, 74uH)
B (28mm ID, 74uH) (*)
C (39mm ID, 74uH) (*)
(*) under qualification.
1. Functional Diagram



MLX90109
VDD
VDD
COIL
MLX90125
C
Tune
2. Description

The MLX90125 encompasses a set of standard
available coils that with a tune capacitor forms
the parallel reader antenna for the MLX90109
reader IC. On top of the high level of integration
of the MLX90109, it further minimizes the
development effort for novice and experienced
users to realize a reader basestation.
The coil is targeted towards lightweight and
compact systems; like portable appliances,
tools,
or
even
access control
systems.
Therefore the physical dimensions are optimized
in weight and size. The coil can be mounted on
a PCB around other mounted components. Or it
can be positioned in any orientation as required
by the application.
The inductance values have been chosen such
that with a single standard capacitor value the
resonance frequency can be realized. Since the
parallel antenna resonance determines the
readers' carrier frequency, special care is taken
to minimize the tolerance on the inductance
value.

3901090125
Page 2 of 7
Aug/02
Rev.001
CONTENTS
FEATURES AND BENEFITS .................................................................................................................. 1
APPLICATIONS ...................................................................................................................................... 1
ORDERING INFORMATION.................................................................................................................... 1
1.
FUNCTIONAL DIAGRAM................................................................................................................. 1
2.
DESCRIPTION ................................................................................................................................. 1
3.
ABSOLUTE MAXIMUM RATINGS ................................................................................................... 3
4.
MLX90125-CZA-A ELECTRICAL SPECIFICATIONS ....................................................................... 3
5.
MLX90125-CZA-A PHYSICAL SPECIFICATIONS (SEE FIG 1.) ...................................................... 3
6.
MLX90125-CZA-B ELECTRICAL SPECIFICATIONS ....................................................................... 3
7.
MLX90125-CZA-B PHYSICAL SPECIFICATIONS (SEE FIG 1.) ...................................................... 4
8.
MLX90125-CZA-C ELECTRICAL SPECIFICATIONS ....................................................................... 4
9.
MLX90125-CZA-C PHYSICAL SPECIFICATIONS (SEE FIG 1.) ...................................................... 4
10.
APPLICATIONS INFORMATION...................................................................................................... 5
A
NTENNA
R
ESONANCE
F
REQUENCY
: ....................................................................................................................5
A
NTENNA
I
MPEDANCE
..........................................................................................................................................5
A
NTENNA CURRENT
. ............................................................................................................................................6
11.
APPLICATION COMMENTS ............................................................................................................ 6
12.
FAQ.................................................................................................................................................. 6
13.
DISCLAIMER ................................................................................................................................... 7

3901090125
Page 3 of 7
Aug/02
Rev.001
3. Absolute Maximum Ratings
Supply Voltage, V
DD
(overvoltage)
V
Supply Voltage, V
DD
(operating)
V
Supply Current, I
DD
mA
Output Current, I
OUT
mA
Operating Temperature Range, T
A
-50
C
Operating Temperature Range, T
S
100
C
Exceeding the absolute maximum ratings may cause
permanent damage. Exposure to absolute-maximum-
rated conditions for extended periods may affect device
reliability.
MLX90125 is qualified for application with MLX90109.
Please refer to MLX90109 datasheet for applicable
absolute maximum ratings.
4. MLX90125-CZA-A Electrical Specifications
Operating Parameters at 125kHz, 1Vac, T = 25
o
C (unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Units
Coil inductance
Lant
71.5
73.7
75.9 uH
Coil Quality factor
Qant
22.5
25
27.5
Antenna impedance
Zant
Calculated = Wres*Lant*Qant
1.26
1.64 kOhm
Self resonance Frequency
SRFcoil
3000
kHz
5. MLX90125-CZA-A Physical Specifications (see fig 1.)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Units
Coil height
H
3
mm
Outside Diameter
OD
18.9 mm
Inside diameter
ID
16.9
17
17.5 mm
Lead length
LL
20
mm
Tin plated Lead end
LE
5
mm
Number of Turns
Nr
52
6. MLX90125-CZA-B Electrical Specifications
Operating Parameters at 125kHz, 1Vac, T = 25
o
C (unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Units
Coil inductance
Lant
71.5
73.7
75.9 uH
Coil Quality factor
Qant
(22)
Antenna impedance
Zant
Calculated = Wres*Lant*Qant
(1.1)
kOhm
Self resonance Frequency
SRFcoil
3000
kHz


3901090125
Page 4 of 7
Aug/02
Rev.001
7. MLX90125-CZA-B Physical Specifications (see fig 1.)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Units
Coil height
H
(3)
mm
Outside Diameter
OD
(29)
mm
Inside diameter
ID
(28)
mm
Lead length
LL
(35)
mm
Tin plated Lead end
LE
(5)
mm
Number of Turns
Nr
(36)
8. MLX90125-CZA-C Electrical Specifications
Operating Parameters at 125kHz, 1Vac, T = 25
o
C (unless otherwise specified)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Units
Coil inductance
Lant
71.5
73.7
75.9 uH
Coil Quality factor
Qant
(22)
Antenna impedance
Zant
Calculated = Wres*Lant*Qant
(1.1)
kOhm
Self resonance Frequency
SRFcoil
3000
kHz
9. MLX90125-CZA-C Physical Specifications (see fig 1.)
Parameter
Symbol
Test Conditions
Min
Typ
Max
Units
Coil height
H
(3)
mm
Outside Diameter
OD
(40)
mm
Inside diameter
ID
(39)
mm
Lead length
LL
(35)
mm
Tin plated Lead end
LE
(5)
mm
Number of Turns
Nr
(36)
H
OD
ID
LL
LE
Fig. 1

3901090125
Page 5 of 7
Aug/02
Rev.001
10. Applications Information
Antenna Resonance Frequency:
The MLX90125 can be applied with a single Tune capacitor in parallel to realize the target resonance frequency as
can be found from :

Fres = 1/sqrt(Lant*Ctune)

For 125kHz we find
C [nF]
12
18
22
27
30
33
L [uH]
135.1
90.1
73.7
60.0
54.0
49.1

When applied with a high Q transponder, the spread on the reader resonance frequency should be minimal, and a
2% capacitor is then recommended. Together with the +/-3% of the coil this yields a 2.5% spread on the resonance
frequency. For application with low Q transponders like the MLX90127, a 5% capacitor giving an overall 3.5%
spread on the resonance frequency is acceptable.

For instance 125kHz +/-3.5% implies a resonance frequency range of [120.6, 129.4]kHz

Temperature drift of the inductance value from -40 to +85C is characterized to be less than 1%.
Antenna Impedance.
The antenna impedance is an important system design parameter for the MLX90109 (see MLX90109 datasheet).
For normal read and write operation Zant = Vant/IDD is minimum 500Ohms, and minimum 1kOhm for auto start up.
The Antenna impedance can be approximated as
Zant = Qant.Wres.Lant
with
Wres = 2
*Fres

We can calculate the minimum Qant to guarantee good operation of the reader. In the table an overview of the
minimum Q is mentioned for realizing a 1.1kOhm at 125kHz. This guarantees auto start up with some process
tolerance.
L [uH]
135.1
108.1
90.1
73.7
54.0
Qant (1.1kOhm)
10.4
13.0
15.6
19.0
25.9

Mind ...
-
That higher Qant reduces the total reader current consumption, but it has no influence on the antenna current.
The latter is directly related with inductance value and the antenna voltage amplitude.
-
That in reality the coupling with the tag may drastically reduce the antenna impedance. For instance when the
MLX90127 is held against (0mm distance) the 18mm reader coil (MLX90125-CZA-A) VMODU has to be
increased to 2V to guaranteed correct read out by the MLX90109 using the 18mm. (see EVB90109)
Temperature drift of the quality factor compared to the reference value at 25C is typically:
-40
o
C: --
+85
o
C: --
(Data to be completed in next revision)
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