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BQ500215EVM-648: About distance between Tx and Rx

Tsukui Yusuke
Guru 21930 points
Part Number: BQ500215EVM-648
Other Parts Discussed in Thread: BQ51025EVM-649, , BQ500215

Hi,

Could you tell me about distance between Tx coil and Rx coil?
My customer is evaluating bq500215evm-648 and bq51025evm-649.
Customer thought that the closer the distance between A and B, the more efficient.
And, Customer removed the acrylic plate and brought it closer.
However, Efficiency has declined.
Please advice about the proper distance of the coil.
5811.bq500215.pdf

Best Regards,
Yusuke / Japan Disty

  • 0
    Guru 21930 points

    Hi,

    Can I get the information?
    I will attach the waveform.
    If you need more information or if  I should  clarify my comment ,
    please let me know.
     
    Best Regards,
    Yusuke/Japan Disty

  • 0 in reply to Tsukui Yusuke
    TI__Guru* 75656 points
    On the TX side the coil to interface distance is 2mm +/- 0.5mm---Specification for MP-A5 medium power TX. Removed the clear cover is not recommended, unit is not designed to operate in this configuration.
  • 0 in reply to Bill Johns
    Guru 21930 points

    Bill-san,

    Thank you for your support.
    I understood said.
    Let me ask you one more thing.

    Do you have materials on distance and efficiency between Tx and Rx?
    Could you give me it?

    Best Regards,
    Yusuke / Japan Disty

  • 0 in reply to Tsukui Yusuke
    TI__Guru* 75656 points
    Hi Yusuke-san
    The efficiency will vary a great deal with the type of RX coil used an how it is mounted (metal around it).
    Efficiency measurements with the EVM over coil to coil distance (Z-distance) will decrease as distance increases. The measurement with EVM performance will not be the same as the final customer product due to the above differences.
    As coil to coil distance is increased TX coil current is increased to generate a larger magnetic field to deliver the same amount of power. Power out is the same but power in will go up. The additional losses fall into two categories.
    Loss in the power section due to higher coil current, switching loss, DCR loss and others.
    Loss due to a larger magnetic field, if the flux line is not broken it is not a loss. But the larger magnetic field can now enter more metal in a larger area and result in higher losses.
  • 0 in reply to Bill Johns
    Guru 21930 points

    Bill-san,

    Thank you for your kind support.
    Your explation is easy to understand.
    Do you have materials or white paper on distance and efficiency between Tx and Rx?
    I want to know formula for your explanation.

    Best Regards,
    Yusuke / Japan Disty

  • 0 in reply to Tsukui Yusuke
    TI__Guru* 75656 points
    Hi Yusuke-san
    A couple of good articles to look at:
    1.) "The Qi Wireless Power Standard" by Dries van Wageningen and Toine Staring
    ieeexplore.ieee.org/.../
    2.) "Wireless Power for Mobile Devices" by Eberhard Waffenschmidt
    ieeexplore.ieee.org/.../