BQ500412 Datasheet, PDF (14/28 Pages) Texas Instruments – Low System Cost, Wireless Power Controller for WPC TX A6

bq500412
SLUSBO2A – NOVEMBER 2013 – REVISED DECEMBER 2013
www.ti.com
Parasitic Metal Object Detect (PMOD), Foreign Object Detection (FOD) and FOD Calibration
The bq500412 supports improved FOD (WPC1.1) and enhanced PMOD (WPC 1.0) features. Continuously
monitoring input power, known losses, and the value of power reported by the RX device being charged, the
bq500412 can estimate how much power is unaccounted for and presumed lost due to metal objects placed in
the wireless power transfer path. If this unexpected loss exceeds the threshold set by the FOD or PMOD
resistors, a fault is indicated and power transfer is halted. Whether the FOD or the PMOD algorithm is used is
determined by the ID packet of the receiver being charged.
As the default, both PMOD and FOD resistors should set a threshold of 400 mW (selected by 56.2-kΩ resistors
from FOD (pin 13) and PMOD(pin 6) to LOSS_THR (pin43)). 400 mW has been empirically determined using
standard WPC FOD test objects (disc, ring and foil). Some tuning might be required as every system will be
slightly different. The ultimate goal of the FOD feature is safety; to protect misplaced metal objects from
becoming hot. Reducing the loss threshold and making the system too sensitive will lead to false trips and a bad
user experience. Find the balance which best suits the application.
If the application requires disabling one function or the other (or both), it is possible by leaving the respective
FOD/PMOD pin open. For example, to selectively disable the PMOD function, PMOD (pin16) should be left open.
NOTE
Disabling FOD results in a TX solution that is not WPC compliant.
Resistors of 1% tolerance should be used for a reliable selection of the desired threshold.
The FOD and PMOD resistors (pin 13 and pin 6) program the permitted power loss for the FOD and PMOD
algorithms respectively. The FOD_CAL resistor (pin 22), can be used to compensate for any load dependent
effect on the power loss. Using a calibrated test receiver with no foreign objects present, the FOD_CAL resistor
should be selected such that the calculated loss across the load range is substantially constant (within ~100
mW). After correcting for the load dependence, the FOD and PMOD thresholds should be re-set above the
resulting average by approximately 400 mW in order for the transmitter to satisfy the WPC requirements on
tolerated heating.
Please contact TI for more information about setting appropriate FOD, PMOD, and FOD_CAL resistor values for
your design.
Table 2. Option Select Bins
BIN NUMBER
0
1
2
3
4
5
6
7
8
9
10
11
12
13
RESISTANCE (kΩ)
<36.5
42.2
48.7
56.2
64.9
75.0
86.6
100
115
133
154
178
205
>237
LOSS THRESHOLD
(mW)
250
300
350
400
450
500
550
600
650
700
750
800
850
Feature Disabled
14
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