User Guide Rev 2.0
www.semtech.com
2 of27
TSDMTX-19V3-EVM
May-18
Semtech
Wireless Charging Concepts
Wireless power transfer is, essentially, a transformer. Current 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.
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
TS80003, which first searches for a receiver. Once found, the receiver informs the transmitter of its power
requirements, and transmission begins. The system then verifies the right amount of power being sent, and that
no power is being lost to foreign objects. The receiver will continually provide ongoing requests for power to
maintain the transaction. If the 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 receiver. If the receiver requires no further power, such as when a battery is fully charged, it
can request no further power being sent, and the transmitter will reduce its output accordingly.
Wireless power systems have been broken into three power categories. “Wearable” devices, such as headsets,
wrist-band devices, medical sensors etc - operate in the low power range, up to 3 watts. Medium power devices, in
the 5- to 15-watt range, include handheld devices, such as cell phones, tablets, and medical electronics. High
power systems support devices such as power tools, radio controlled (“RC”) devices such as drones, and other
equipments requiring 15 to 100 watts of power.
Receiver
Transmitter
Co
nt
ro
l
Electromagnetic
Flux
Controller
FET Array
Power
Supply
Supply
Regulation
Rectifier
End
Equipment
Po
w
er
