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Tiny Wireless Receiver design data

Sammy Peiren62
Intellectual 310 points
Other Parts Discussed in Thread: BQ51050B

Hello,


We are designing a wireless power system with the BQ51050B for a small wearable device. We have selected a coil which TI have also used in the tests for the reference design  (see TIDA-00329 Test Report). The coil is Wϋrth 760308101303. We have calculated C1=56nF and C2=560pF for the capacitors in the resonant LC circuit. The system was tested with a TI TESLA transmitter, but we are getting extremely small working distances. If plastic is inserted between the two coils the receiver fails to start up. Can you share the values you used for the tests in TIDA-00329 with the same coil? What working distance did you achieve with that coil?

  • 0
    TI__Guru 65846 points

    I will check the test data and get back to you.

    To calculate C1 did you used the L from data sheet, 47uH or measure with RX coil Test Fixture (see data sheet).  I would expect the L value to be closer to 30uH when placed on the test fixture. This would put the C1 value closer to 100nF.

    Also what distance are you testing with?

  • 0 in reply to Bill Johns
    Intellectual 310 points

    Hello Bill, thank you for the fast response. Indeed we used 47µH for both Ls and Ls'. We do not have the ferrite sheet available at the moment and TDK doesn't seem to produce PC44 material anymore. I will try changing C1 to a higher value and check the effect. 

    Our working distance is about 5mm (the plastic from the Tesla transmitter + the plastic casing from the BQ51050b-EVM).


    With just the plastic from the Tesla transmitter (I think that's about 3mm) we do get a proper connection, but in reality the coil will be put in a plastic enclosure too, so we need at least 5mm. Will the resonance have a large effect on the distance? I would expect the main factor to be the size of the Rx coil.

  • 0 in reply to Sammy Peiren62
    Intellectual 310 points

    Bill, any news on the data? We have done some more tests using different capacitors, but we still can't get it to work at larger distances.