We would like to use the WPC to detect receiver presence at all times, not just during active charging.
We have considered using these techniques because does not appear the standard easily supports this feature:
1.) using FOD to detect receiver during full charge or power off state.
e.g. Detect = FOD || charging.
Does the FOD have any analog resolution to determine the size/proximity of the receiver.
2.) actively adjusting the charge rate so battery never fully charged and never exits charging state where. Presuming most receivers will request the charge rate based on their state of charge we could scale down delivered power, even to the point where device is net discharging e.g. (charging rate < idle power consumption)
To evaluate we read the standard and have these following misc questions:
p.72: If a Power Receiver has made at most three unsuccessful attempts to initiate and maintain power transfer—e.g. has terminated the power transfer three times in a row with an End Power Transfer Packet containing an End Power Transfer Code of 0x01 (Charge Complete), 0x07 (Reconfigure), or 0x08 (No Response)—the Power Transmitter shall refrain from entering the power transfer phase until the Power Receiver has been removed from the Interface Surface of the Base Station.
Could device discharge on the charging pad without any top off, until it is removed and replaced on pad?
p.81 The Power Receiver may stop transmitting Packets to the Power Transmitter at any time. This behavior causes the Power Transmitter to remove the Power Signal, possibly under the assumption that a user has removed the Power Receiver from the Interface Surface. The recommended behavior to cause the Power Transmitter to remove the Power Signal (when a user has not removed the Power Receiver from the Interface Surface) is to transmit an End Power Transfer Packet as defined in Sections 5.3.2 and
Does TI anticipate most devices will follow the recommended behavior of responding to ping even at full charge?
FOD cannot be used to detect RX full charged and on the TX.
TS-CTRL can be used to send charge complete, see data sheet.
Bill Johns, Applications Engineer
bqTESLA Wireless Power Products
Texas Instruments Inc
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