BQ500110_11 Datasheet, PDF (14/25 Pages) Texas Instruments – Qi Compliant Wireless Power Transmitter Manager

bq500110
SLUSAE0A – NOVEMBER 2010 – REVISED APRIL 2011
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Parasitic Metal Object Detection (PMOD)
As a safety feature, the bq500110 can be configured to detect presence of a parasitic metal object placed in the
vicinity of the magnetic field. The BQ500100 uses the Rectified Power Packet information and the measured
transmitter input-power to calculate parasitic losses in the system. When an excessive power loss is detected the
device will lit the red LED to warn about this undesirable condition, If during a twenty second warning time the
parasitic metal object was not removed , the controller will disable power transfer. After being in halt for five
minutes bq500110 will attempt normal operation. If the object that caused excessive power dissipation is still
present, the sequence will be repeated over and over again. If the metal object is removed during this twenty
second warning time, the normal operation will be restored momentarily.
To facilitate parasitic loss function, the bq500110 monitors the input voltage and the input current supplied to the
coil power drive circuit.
The PMOD_THR pin is used to set the threshold at which the MOD is activated. The MOD operation can be
disabled by selecting the highest bin( leaving the pin is left floating).
The threshold is set by Equation 2:
Threshold = 1400 mW + Bin_Number x 100 mW
(2)
Note: The WPC Specification V1.0 does not define the requirements and thresholds for MOD feature, thus metal
object detection may perform differently with different products. Therefore make your own decision when setting
the threshold. In most desktop wireless charger applications setting the PMOD threshold to 1.5W shown to give
good results in stopping power transfer and preventing small metal objects like coins, pharmaceutical wraps, etc.
getting hot when placed in the path of wireless power transfer. Figure 1 depicts PMOD performance measured
on bq500110 EVM. .
APPLICATION INFORMATION
Typical application diagrams for the WPC 1.0 compliant transmitter are shown on the following pages.
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