Standard Use ...............................................................................................................................................4
Next Steps..................................................................................................................................................16
Wireless Charging
User Guide
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Wireless Charging Concepts
Wireless power transfer is, essentially, a transformer. Power is provided to a primary coil which produces an
electromagnetic (EM) field. In this field, a secondary coil is placed. The EM field induces a current into the
secondary coil, providing power to whatever it is connected to.
However, unlike a conventional power transformer that operates at line frequencies and requires an iron core for
efficiency, wireless power systems are designed to operate in the 100 kHz range, and thus can perform efficiently
with an air core. As such, the primary and secondary windings, if closely spaced, can be in separate devices, the
primary being part of a transmitter and the secondary within a receiver. This implementation can also be described
as a radio broadcast process, and as such, these transformer coils can also be seen as antennas with equal validity,
and the two terms will be used interchangeably in this text.
Receiver
End
Equipment
Supply
Regulation
Rectifier
Control
Power
Transmitter
Power
Supply
Controller
FET Array
Electromagnetic
Flux
Wireless power systems differ in another major aspect from conventional transformers, in that they are
intelligently managed. A transmitter will only provide power when a receiver is present, and only produce the
amount of power requested by the receiver. In addition, the system is capable of recognizing when the
electromagnetic field has been interrupted by an unintended element, a 'foreign object', and will shut down the
transfer to prevent any significant amount of power being absorbed by anything but a proper receiver. The
intelligent management of the wireless power transmission process is achieved though the programming of the
TS81000. When introduced to a compliant transmitter, the TSDMRX-19V20W-EVM receiver informs the
transmitter of its power requirements, and transmission begins. The receiver then verifies the right amount of
power is being sent, and that none is being lost to foreign objects. The receiver continually provides ongoing
requests for power to maintain the transaction. If these requests cease, the transaction terminates. Via this
protocol, even complex charging patterns can be supported, as the transmitter can provide varying amounts of
power at different times, as requested by the TSDMRX-19V20W-EVM. Should the TSDMRX-19V20W-EVM require
no further power, such as when a battery charge is completed, it can request no further power be sent, and the
transmitter will reduce its output accordingly.
Wireless power systems have been broken into three basic power categories. “Wearable” devices, such as
headsets, wrist-band devices, medical sensors, and so forth - all operate in the low power range, up to 5 watts.
Medium power devices, in the 5- to 15-watt range, include most handheld devices, such as cell phones, tablets,
and medical electronics. High power wireless systems are intended to support devices such as power tools, radio
controlled (“RC”) devices such as drones, and other equipment requiring 15 to 100 watts of power.
Wireless Charging
User Guide
TSDMRX-19V20W-EVM
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Product Description
The TSDMRX-19V20W-EVM Evaluation Module is a ready-to-use demonstration platform allowing testing of up to
20 watts of wireless power transmission using a proprietary communication protocol as well as backward
compatiblity with the industry inductive standard to charge devices at 15W or below. For 20 watts operation, the
transimitter must be be paired with Semtech’s Transmitter
TSDMTX-19V2-EVM (firmware version should be 004F
or newer),
which can allow a variety of experiments to easily be performed in order to learn more about the
behavior of the system.
To develop your own board, or integrate this functionality into an existing system, the EVM can be used as a
starting point for the design, as it demonstrates a working model from which to proceed. Toward this end, all
documentation for the EVM is provided to make the process as efficient as possible.
The key technology components of the EVM are a trio of Semtech integrated circuits, the TS81000, TS94033, and
TS30042. The TS81000 provides the Qi compliant communications and control for wireless receivers of up to 40
watts. All the intelligent management of the process is handled by the TS81000. Up to 20 watts of power acquired
from the receiver antenna is rectified to 21.5-28.0 VDC. The TS94033 senses the DC current. The TS30042 is the
final part of the process, where the output of the rectification is converted to 19VDC for output to the system load.
This EVM presents a working example of how these three components can be used together to form a complete
wireless power receiver solution with high efficiency, low part count and minimized space requirements.
As seen in the photo below, at the left is antenna leads and the right port can be used to provide output power to
a device. In a 31x16mm portion of the board is the receiver, indicating the size of the actual receiver system. Right
down delow is the connector for programming. Some will be employed in the following text; all are documented
in the schematic diagram below.
In the following section, an introduction will be provided to the evaluator for how to use the EVM for wireless
power reception as well as how the TSDMTX-19V2-EVM can be used in conjunction with.
Wireless Charging
User Guide
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Semtech
Standard Use
The TSDMRX-19V20W-EVM is very easy to use. Start by applying power to the TSDMTX-19V2-EVM transmitter. A
few times each second, the transmitter emits a ‘ping’ of energy in search of a compliant receiver in range - in this
document, the TSDMRX-19V20W-EVM.
Place the TSDMRX-19V20W-EVM over the target area of the transmitter EVM. The TSDMRX-19V20W-EVM is
initially powered by the ping sufficiently to be able to announce its presence to the transmitter, and a transaction
begins. The transmitter next provides a small amount of power to the newly discovered receiver, so the TSDMRX-
19V20W-EVM can tell the transmitter what its power requirements are.
At the completion of this handshake, the transmitter begins providing the requested power, indicated by a green
LED on the receiver EVM. During power transfer, the TSDMRX-19V20W-EVM continuously communicates with the
transmitter, actively directing the process. In this way, it is assured that power is only sent when and how it is
required by the receiver. If required by the load, the TSDMRX-19V20W-EVM can actively increase or decrease its
power request, and the transmitter will act accordingly. As such, equipment with complex charging requirements
can be precisely supported by the TSDMRX-19V20W-EVM and only the desired amount of power is provided. If at
any time an error is detected, transmission is halted. To restart, the TSDMRX-19V20W-EVM must be removed from
the range of the transmitter and returned to the target zone to start a new transaction.
The receiver EVM can deliver up to 20 watts of power at 19 volts to any load the user would like to experiment
with. For general experimentation, the optimal load to select would be a Programmable DC Electronic Load. A
‘load box’ can easily be set to draw a selected current or power at the turn of a knob, making them very flexible
and easy to use in observing power supply operation in general. If a load box is not available, a power resistor
decade box is nearly as convenient, as it can easily be set to any desired resistance to simulate a range of load
conditions. In either case, be sure the test load is rated for at least the amount of power being tested.
Run wires from the VOUT+ and - pins of the receiver EVM to the selected test load, as per the illustration below.
Once the load is added, the receiver EVM can be used to perform a variety of tests.
Note:
In-band communication between the RX and the TX is done using load modulation. At light loads a minimum
load is generated using R15, but that may not be enough to maintain optimal communication.
An external load of
100-200mA is necessary to prevent communication dropouts.
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