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bq51050 -- design question

alex ch70
Prodigy 120 points

hi all.

I’m using bq51050 for new design..

I have several questions...

 

  1. in the datasheet page 25 equation number 5..
    "is to be placed on top of this surface and the inductance is to be measured at 1-V RMS and a frequency of 100 kHz. This measurement is termed Ls’. This measurement is termed Ls or the free-space inductance. Each capacitor can then be calculated using Equation 5 what exactly is Ls' ?

  2.  supposing Ls' is the inductance of the receiving coil that measured in 1V at 100khz, did i have to do this experiment to calculate C1,C2 ( in case that i don’t want to use the specified inductor from the EVM...)

  3.  in case that I’m want to use a PCB build in coil (47uH)( I have reference design only for this value)  and i don’t have the capability to do this experiment, can i estimate the C1,C2 values ? how big the error will be?

  4.  What is the max distance between the RX and TX ? and how I can enlarge this distance..

  5.  What is the resonance frequency ?

  6.  can you please explain the way that  LS’ measured , the exact experiment that need to be done..

thanks for responding .

  • 0
    TI__Intellectual 1122 points

    Hello Alex,

    Ls´  is the inductance of the RX coil measured at 1-V RMS and at a frequency of 100kHz while it is placed on the TX with the z-height (distance) of your end application. If you plan to design your own coil or choose a different one than used for the EVM then  you will have to do this Ls´ measurement. The Ls´ measurement can be done with a LCR meter and the above mentioned settings.

    This article is a good source of information: www.ti.com/.../slyt479.pdf

    The calculation gives you a good starting point for the coil design but the results and final values have to be verified at the bench. Keep in mind that using a PCB coil decreases your system efficiency.

    The distance dz between the TX and RX of up to 5mm is specified by the Wireless Power Consortium. A higher distance will decrease your coupling factor and your system is probably not WPC compliant.

    TX and RX coil circuits are tuned for 100kHz (resonance frequency).


    Best Regards,

    Markus Fleck