BQ51221 datasheet(28/50 Pages) TI2

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WPC v1.2 Transmitter is tested to see if it can detect reference Foreign Objects with a Reference receiver.

WPC v1.2 Specification will allow much more accurate sensing of Foreign Objects.

8.3.17 Receiver Coil Load-Line Analysis

When choosing a receiver coil, TI recommends analyzing the transformer characteristics between the primary

coil and receiver coil through load-line analysis. This will capture two important conditions in the WPC system:

• Operating point characteristics in the closed loop of the WPC system.

• Instantaneous transient response prior to the convergence of the new operating point.

An example test configuration for conducting this analysis is shown in Figure 8-16:

Figure 8-16. Load-Line Analysis Test Bench

Where:

• VIN is a square-wave power source that should have a peak-to-peak operation of 19 V.

• CP is the primary series resonant capacitor (for example, 100 nF for Type A1 coil).

• LP is the primary coil of interest (such as, Type A1).

• LS is the secondary coil of interest.

• CS is the series resonant capacitor chosen for the receiver coil under test.

• CD is the parallel resonant capacitor chosen for the receiver coil under test.

• CB is the bulk capacitor of the diode bridge (voltage rating should be at least 25 V and capacitance value of at

least 10 µF)

• V is a Kelvin connected voltage meter

• A is a series ammeter

• RL is the load of interest

TI recommends that the diode bridge be constructed of Schottky diodes.

The test procedure is as follows

• Supply a 19-V AC signal to LP starting at a frequency of 210 kHz

• Measure the resulting rectified voltage from no load to the expected full load

• Repeat the above steps for lower frequencies (stopping at 110 kHz)

An example load-line analysis is shown in Figure 8-17:

BQ51013B

SLUSB62D – MARCH 2013 – REVISED SEPTEMBER 2020

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BQ51221 Datasheet(PDF) 28 Page - Texas Instruments