Test Setup
6.3.9
Foreign Object Detection (FOD)
The bq50002 EVM supports FOD in order to meet the requirements of the WPC V1.2 specification.
Continuously monitoring input power, known losses, and the value of power reported by the receiver
device being charged, the bq500511 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 resistors, a fault is indicated and power transfer is halted.
Three key measurements for the TX FOD calculation:
•
Input Power
– Product of input voltage and current. Input voltage is measured at BQ500511 pin 9
though R13 and R14. Input current is measured using sense resistor R18 at BQ50002 pin 29 and 30.
Both measurements must be very accurate.
•
Power Loss in Transmitter
– This is an internal calculation based on the operating point of the
transmitter. The calculation is adjusted using FOD_CAL resistor, R26. This calculation changes with
external component changes in the power path such as resonant capacitors and TX coil. Recalculation
of R26 and R27 is required.
•
Receiver Reported Power
– The receiver calculates and reports power it receives in the message
packet Received Power Packet.
The FOD threshold on the EVM is set to 400 mW when R27 is set to 100 k
Ω
. Increasing R27 increases
the threshold and reduces the sensitivity to foreign objects. This loss threshold is determined after making
a measurement of transmitter performance using a FOD calibration receiver similar to a unit manufactured
by Avid
®
Technology. Contact Texas Instruments for the FOD calibration procedure for the bq50002.
6.3.10
Thermal Performance
This section shows a thermal image of the bq50002EVM-607. A 1000-mA load is used at the receiver
output, bq51013BEVM-764. Output power is approximately 5 W, 1 A at 5 V. The highest temperature point
in
is 35.6°C
Figure 7. Thermal Performance
17
SLVUAJ7 – October 2015
bq50002 Wireless Power TX EVM
Copyright © 2015, Texas Instruments Incorporated
