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bqTESLA FAQ----Transmitter FOD-PMOD
Bill Johns
FOD and PMOD
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Foreign Object Detection (FOD)
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WPC version 1.1 of the specification introduces FOD
This adds a level of protection to the WPC system
Backwards compatibility with WPC 1.0 system is not compromised
A WPC 1.1 RX/TX will work with WPC 1.0 TX/RX
A WPC 1.1 system will be able to
• Detect a foreign object that is placed in the magnetic field
• Prevent this foreign object from getting too hot
A WPC RX and TX must be certified with the new certification procedures
Parasitic Metal Object Detection (PMOD)
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TI TX solutions provide safety feature against metal object heating for WPC 1.0 RX. We refer
to this feature as PMOD.
This adds a level of protection to the WPC system
Interoperability with WPC 1.0 certified RX is not compromised
This is a PROPRIERARY implementation
The PMOD algorithm does depend on Receiver RECT_PWR being approximately in the
correct range.
TI TX solutions allow the end-user to independently configure FOD & PMOD thresholds.
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WPC System / Power Loss Accounting
FO
PWR
FO
TX PWR
V-in / I-in
RX PWR
TRANSMITTER
PTX  Pin  LOSSTX
RX
Received Power
Packet
PFO  PTX  PRECEIVED
If PFO  THRESHOLD  then FO is present
TX PWR – Transmitted Power---Power leaving TX interface surface
RX PWR – Received Power--Power entering the RX interface surface
FO PWR – Energy absorbed by Foreign Object (FO)
WITHOUT FOREIGN OBJECTS
TX PWR = RX PWR
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WITH FOREIGN OBJECTS
TX PWR = RX PWR + FO PWR
TI WPC1.1
– Transmitters are characterized to understands their losses & actual “Transmitted Power”
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Transmitter uses V-in and I-in to calculate input power and operating point to calculate loss
Receivers are characterized to understands their losses & actual “Received Power”
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Receivers send this info to Transmitter in “Received Power” packet
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Recommended FOD Threshold setting
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ENABLE both FOD & PMOD feature w. Independent
threshold
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THREE resistors are used to set three values:
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Single resistor R-LOSS configuration for
combined THRESHOLD for FOD/PMOD is
NOT RECOMMENDED.
– R_FOD between pin17 and pin34 sets FOD
– R_PMOD between Pin16 and pin34 sets FOD
– R_CAL between pin15 and pin34 sets FOD_CAL.
Omitting R_PMOD will disable the PMOD function.
Omitting R_FOD will disable the FOD function.
Omitting R_CAL will result in the default FOD_CAL
setting which MAY not result in compliance FOD
algorithm for a give system.
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Key advantages w. this configuration includes:
– WPC 1.1 Compliance
– Additional protection for WPC 1.0 RX
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When we enable PMOD, there is a potential
concern for interoperability issues w. some
certified WPC 1.0 RXs
For Further Reference – resources available on-line
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TI Wireless Power Landing Page: www.ti.com/bqtesla
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Application Notes and Articles on TI Website (type in literature number – “SLxxx”
into the search window at www.ti.com to access each document):
– SLUA649: “bqTESLA Transmitter Coil Vendors” Application Note
– SLUA635A: “Building a Wireless Power Transmitter”
– SLYT477: “Qi-compliant Wireless Power Receiver Coil Design Guidelines”
article in TI Analog Applications Journal (Q3 2012)
– SLYT399: “An introduction to the Wireless Power Consortium standard and
TI’s compliant solutions” TI Analog Applications Journal (Q1 2011)
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“Universally Compatible Wireless Power Using Qi Protocol”
– http://www.low-powerdesign.com/article_TI-Qi.html
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http://www.wirelesspowerconsortium.com/