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BQ51050B Parameters Definition

Rahul Soni17
Prodigy 240 points

Other Parts Discussed in Thread: BQ51050B

Hi,

I am designing BQ51050 to charge a 300mAh battery. In the datasheet of BQ51050B, page no 30, can you please tell me what is the difference between L's and Ls. Also, Fs is 100KHz and Fd is 1MHz, how did you get these numbers. 

  • 0
    TI__Genius 14890 points

    Rahul,

    Figure 34 in the bq51050B datasheet (just above formula 6, shows a drawing of the fixture required to measure Ls'.  Ls is simply the inductance of the coil. Ls' is the inductance measured with the fixture. The picture below is shows the measurement.

    The ferrite material and measurement requirements (100kHz and 1MHz) come from the Wireless Power Consortium specification.

    A good way of approximating the Ls' is to measure the inductance when the receiver coil is placed on the transmitter to be used in normal operation.  The values may not be exact, but will allow calculation of Cs and Cd.  The final solution may need some minor changes in the Cs and Cd values.  The efficiency at different Cs values is a good indication of fit.

    Regards,

    Dick

  • 0 in reply to Dick Stacey
    Prodigy 240 points

    Hi DIck.

    Thanks for your response.
    I am afraid to calculate L's as I'm going to purchase the coils after project completion. Right now we are in component selection phase. Can you suggest me to choose any appropriate value of L's if Ls is 26uH.

    Also, If I refer to the "Wireless Power Coil Consideration" from WURTH ELEKTRONIK, then they have chosen Ft(tuned frequency)= 127Khz and Fd(detuned frequency)= 142Khz and if I go with these values, then the values of Cs and Cd will be changed. Below is the link for WE doc. Can you please suggest me what values I must choose.

    www.we-online.com/.../WPCC_changing_considerations_15k_9images.pdf

    Also, can you please provide me "Wireless Power Consortium specifications" for further designing consideration

  • 0 in reply to Rahul Soni17
    TI__Genius 14890 points

    Rahul,

    Ls' is not a value that can be estimated based on Ls.  There are too many factors that influence the Ls' value, including shielding material, distance between RX and TX, material between RX and TX, other metals in the area and other factors.

    That being said, starting with an Ls of 26uH, you could estimate 30uH for Ls'.  Again, this value could be off significantly depending on the factors mentioned above.  This sets the resonant frequency of the RX system - with a goal of 100kHz to match the resonant frequency of the TX.

    The 127kHz mentioned in the article you linked to is not the resonant frequency of the system.

    You would need to contact the Wireless Power Consortium for any documents from them.

    Regards,

    Dick