Datasheet

Ls’

bq51013B

www.ti.com

SLUSB62A –MARCH 2013–REVISED OCTOBER 2013

WPC 1.1 Compliance – Foreign Object Detection

The bq5101xB is a WPC 1.1 compatible device. In order to enable a Power Transmitter to monitor the power

loss across the interface as one of the possible methods to limit the temperature rise of Foreign Objects, the

bq5101xB reports its Received Power to the Power Transmitter. The Received Power equals the power that is

available from the output of the Power Receiver plus any power that is lost in producing that output power (the

power loss in the Secondary Coil and series resonant capacitor, the power loss in the Shielding of the Power

Receiver, the power loss in the rectifier). In WPC1.1 specification, foreign object detection (FOD) is enforced.

This means the bq5101xB will send received power information with known accuracy to the transmitter.

WPC 1.1 defines Received Power as “the average amount of power that the Power Receiver receives through its

Interface Surface, in the time window indicated in the Configuration Packet”.

In order to receive certification as a WPC 1.1 receiver, the Device Under Test (DUT) is tested on a Reference

Transmitter whose transmitted power is calibrated, the receiver must send a received power such that:

0 < (TX PWR)

REF

– (RX PWR out)

DUT

< –250mW (5)

This 250mW bias ensures that system will remain interoperable.

WPC 1.1 Transmitter will be tested to see if they can detect reference Foreign Objects with a Reference receiver.

WPC1.1 Specification will allow much more accurate sensing of Foreign Objects.

Series and Parallel Resonant Capacitor Selection

Shown in Figure 2, the capacitors C1 (series) and C2 (parallel) make up the dual resonant circuit with the

receiver coil. These two capacitors must be sized correctly per the WPC v1.1 specification. Figure 41 illustrates

the equivalent circuit of the dual resonant circuit:

Figure 41. Dual Resonant Circuit with the Receiver Coil

Section 4.2 (Power Receiver Design Requirements) in Part 1 of the WPC v1.1 specification highlights in detail

the sizing requirements. To summarize, the receiver designer will be required take inductance measurements

with a fixed test fixture. The test fixture is shown in Figure 42:

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