Test Setup
To install the shield:
Remove clear plastic cover and hardware. Install the PWR633 filter using metal hardware provided. The
filter is grounded though the metal hardware to the TX coil area.
Circuit changes:
EMI_Shield select pin 21 ground = no shield, high(3.3V) = shield
FOD_CAL R52 no shield = 16.2 k
Ω
, shield = 8.06 k
Ω
NOTE
: if ONLY EMI behavior is to be evaluated with the addition of the shield, then circuit changes are
not required.
6.2.2.7
Configuration Resistor
Some functions can be configured by an external resistor pull up and connections, see the data sheet
(
) for more info:
1. Coil Select R58 and R57, configure for type of coil used
2. Shield / no shield Pin 21, configure for shield or no shield
3. Operating freq pin 26, R70 and R69, option to reduce operating range
6.2.2.8
Thermal Protection, NTC
Thermal protection is provided by an NTC resistor network is connected to pin 2. At 1 V on the sense side
(U10-2), the thermal fault is set, and the unit is shut down, The status LED, D7, illuminates red. The
system tries to restart in 5 minutes.
6.2.2.9
Foreign Object Detection
The bq500414Q EVM incorporated the Foreign Object Detection (FOD) call in WPC 1.1. Power loss is
calculated by comparing the power sent to the receiver (RX) with the power the RX reported receiving,
less know power loss. The transmitter determines the power sent to the RX by measuring input power and
calculating internal losses. The RX measures the power it received and also calculates losses. The RX
sends this information to the driver (TX) in a digital word, message packet. Unaccounted for power loss is
presumed to be a foreign object on the charging pad. Should this lost power exceed the threshold set by
R34, a FOD fault is set and power transfer is stopped.
Three key measurements for the TX FOD calculation:
•
Input Power
– Product of input voltage and current. Input voltage is measured at pin 45 though R33
and R31. Input current is measured using sense resistor R64 and current sense amp U9. 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, R52. This calculation changes with
external component changes in the power path such as MOSFETs, resonate capacitors, and TX coil.
Recalculation of R52 and R3 is required.
•
Receiver Reported Power
– The receiver calculates and reports power it receives in the message
packet “Received Power Packet (0X04)”.
The FOD threshold on the EVM is set to 550 mW, R3 is set to 86.6 k
Ω
. Increasing R3 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 the unit manufactured by Avid
®
Technology. Contact Texas Instruments for
the FOD calibration procedure for bq500414Q.
6.2.2.10
WPC Certification
The bq500414QEVM-629 was tested and certified to WPC version 1.2.
15
SLVUA40A – March 2014 – Revised January 2015
bq500414Q bqTESLA Wireless Power TX EVM
Copyright © 2014–2015, Texas Instruments Incorporated