BQ500414Q Datasheet, PDF (13/34 Pages) Texas Instruments – Qi Compliant Wireless Power Transmitter Manager

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bq500414Q
SLUSBE4B – JANUARY 2014 – REVISED JUNE 2014
8.3.8 Foreign Object Detection (FOD) and Parasitic Metal Object Detect (PMOD) Calibration
The bq500414Q supports improved FOD (WPC v1.1) and enhanced PMOD (WPC v1.0) features. Continuously
monitoring input power, known losses, and the value of power reported by the Rx device being charged, the
bq500414Q 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. The ultimate goal of the FOD feature is 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 (pin 6) should be left open.
NOTE
Disabling FOD results in a Tx solution that is not WPC 1.1 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 FOD reference 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.
Contact Texas Instruments for the Tx Tuning Tool to set 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
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