Rx COIL FOR HIGH FREQUENCY WIRELESS POWER TRANSFER
Product Name
Wireless Charging Coil - High Frequency Receive
Molex PN
1461798021
Part Description
Wireless Charging Coil - High Frequency Receive
REVISION:
ECR/ECN INFORMATION: TITLE:
EC No:
111410
DATE:
2016/12/28
CREATED / REVISED BY:
Rx COIL FOR HIGH FREQUENCY WIRELESS
POWER TRANSFER
CHECKED BY:
SHEET No.
B
1
of
6
APPROVED BY:
DOCUMENT NUMBER:
AS-1461798021
Benson Liu 2016/12/28
power transfer
Ryan Liu 2016/12/28
Welson Tan 2016/12/28
Molex P/N 146179 8021
High Frequency Low Power Rx
`
Rx COIL FOR HIGH FREQUENCY WIRELESS POWER TRANSFER
FEATURES
•
Industry’s highest FPCB Q Factor
•
Wearable and small form factor design
•
Industry leading thinness of 0.685mm MAX
(w/shield)
•
Enables high efficiency solutions
•
Flex construction:
Increased durability
Repeatable performance
Integration with other electronics
•
Custom design available
Molex Part Number
1461798021
Electrical Parameters at 25
o
C
Inductance
+/-2%, @
6.78 MHz (uH)
4.0
DCR
+/- 2%
(mOhm)
235
ESR
+/- 2%
(mOhm)
1450
Mechanical Parameters (mm)
Assembly
Thickness
(w/shield)
0.685 MAX
Quality
factor
115
Coil
Thickness
0.24
Material
Flex
www.molex.com
Rev B 01/03
Molex P/N 146179 8021
High Frequency Low Power Rx
`
GENERAL DESCRIPTION:
This specification describes a FPCB receiver coil for wireless power transfer at frequencies 6.78 MHz.
The information in this document is for reference and benchmark purposes only. The user is
responsible for validating coil performance based on users own testing environment.
PRODUCT DESCRIPTION:
This high efficiency coil is designed for high performance wearable or any other device / accessory
requiring up to 2.5W power out. Standard FPCB construction enables integration with other
electronics, high durability, and consistent performance.
DEFINITIONS:
Equivalent Series Resistance
(ESR): resistance measured at or around the operating frequency.
ESR accurately characterizes any losses such as skin effect or proximity effect and any additional
effects that may occur in the presence of material such as shielding, metal backing, or the housing.
Comparison of coil assembly and in situation ESR measurements can accurately determine sources
of loss. This metric should be given serious consideration during product selection to ensure full
characterization of system electrical parameters.
Direct Current Resistance
(DCR): resistance measured at DC or measured at very low frequencies
(60 Hz - 100 Hz) and is often considered an incomplete measurement in wireless charging
environments because it does not take into account actual causes of resistance during operation.
NuCurrent recommends ESR as the most relevant measurement of resistance in a wireless power
coil, but provides DCR values as well.
PRODUCT TUNING:
It is important to optimize the tuning circuit for every application. Improper tuning can lead to inferior
system performance even if the individual system blocks, including the coil, comprise high
performance components.
The objective of the matching circuit is to resonate the inductive coil (Z
COIL
) and match it to Z
IN
(See
diagram below). Z
IN
may be variable; for example when charging a battery, there is a swing in the
Z
LOAD
value which may translate to a swing in Z
IN
. Instead of optimizing for the full swing in Z
IN,
a
relatively straightforward approach to keep losses low may be to match for maximum efficiency when
Z
IN
is at full load (peak power draw).
A generic tuning/matching network (C1, C2, C3) is provided below as a typical system for wireless
charging using magnetic resonance coupling. The topology is a shunt-series-differential-capacitor
network. Depending on the application, choice of ICs, effective self-Inductance of the coil (L
EFF
), and
coupling with the transmitter, a derivative topology (e.g. single-ended series, differential series, etc.)
may also be implemented.
www.molex.com
Rev B 01/03
Molex P/N 146179 8021
High Frequency Low Power Rx
`
With regards to the capacitor-network, the choice of topology is dependent on the desired V
RECTIFIER
and the receiver coil selection. A good rule of thumb to determine the
relative
V
RECTIFIER
between
different receive coils is to compute the product L
EFF
x A
EFF
, where A
EFF
is the effective area of the
coil. Series tuning is typically preferred for high L
EFF
coils with good coupling (to the transmitter) to
induce a V
RECTIFIER
within the desired range (typically 7V - 15V for a 4W - 7W receiver). Shunt tuning
can be used with very low L
EFF
coils with low coupling. In general, the shunt helps boost the V
RECTIFIER
.
Shunt-series tuning may be used for coils which demonstrate intermediate coupling with the
transmitter; this topology also offers more flexibility towards designing for Z
IN
.
SMT inductors (not shown) may be added in series with C2 and/or C3 to block high frequency
harmonics. An EMI filter may also be utilized to prevent harmonics generated at the rectifier stage to
re-enter the wireless link.
In order to account for the effect of the environment on the coil, all measurements, including Z
COIL
,
should be performed in-situ, i.e. the coil assembly placed in its intended location in the end
application.
Finally, the choice of the matching topology and filtering components is a function of the desired
performance, complexity and BOM.
For detailed product specific tuning information, please contact Molex at
www.molex.com
or via phone
1 800-78MOLEX (1 800 786-6539).
www.molex.com
Rev B 01/03
Molex P/N 146179 8021
High Frequency Low Power Rx
`
PERFORMANCE:
For custom applications, Molex and NuCurrent can optimize antenna assemblies for thickness, price
or efficiency. The data below demonstrates the performance of the coil up to 2.5W.
•
•
•
A Certified Class 2 transmitter used for all tests
Tests done with receiver located in the center of Transmitter
End-End Efficiency is defined as Rectified Power/Input Power
www.molex.com
Rev B 01/03
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