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Design modification for TIDA-00318

Other Parts Discussed in Thread: TIDA-00318, BQ51003

Hello,

I want to use the TIDA-00318 reference design in my new project, but the coil I have to use is WR121210-27M8-ID (8.32µH Wireless Charging Coil Receiver 950 mOhm 0.472" Dia x 0.013" H (12.00mm x 0.32mm)). 

How can I modify the reference design to accommodate for this coil ? Can I modify it to work with other coils ? I need to know the components value difference so I can use this design with  BQ51003 + BQ25100 combo to charge my coin cell battery(ML-2020/H1CN). 

Please help me find a solution. Thank you very much.

Best regards,

Summaiya Siddiqui

  • Summaiya,

    The TIDA-00318 reference design can be modified to work with many different coils.  The only change required is in the Cs and Cd capacitors.  This would be C1, C2, C3, C4 and C5 in the reference design schematic.  They will be changed to set the resonant frequency based on the new coil.

    The discussion on the correct values for the bq51003 is in the datasheet section 9.2.0.2.2 "Series and Parallel Resonant Capacitor Selection".  Figure 33 shows the Series (C1) and parallel (C2) capacitors for tuning.  Equation 6 has the calculations required.

    Regards,

    Dick

  • Hello Dick,

    Thank you very much for your response. I just want to confirm some points:

    So I have basically used the schematic of TIDA-00318 reference design in my project and I will try to charge my battery with it. However, in the bq51003 datasheet section 9.2.1  "bq51003 Wireless Power Receiver Used as a Power Supply", the figure displays a host connection. I have not connected any pin to my processor. Do I absolutely need to do that ? 

    Please guide me here. Thank you very much.

    Best regards,
    Summaiya Siddiqui

  • Also, please confirm that as stated in the section "Series and Parallel Resonant Capacitor Selection", in order to get the values of these Capacitor, I have to buy the text fixture material and perform this test to get the inductance value? Is there any other way to get these C values ?

    Please let me know. Thank you very much.

    Best regards,
    Summaiya Siddiqui
  • Summaiya,

    The bq51003 does not need a host. The host would be used to monitor the CHG pin and control the EN1 and EN2 pins. As in the TIDA-00318, the EN pins are tied low and the CHG is left floating.

    You can put the coil on the transmitter and get a good approximation of the Ls' using an LCR meter to measure the inductance.

    Dick
  • Hi Dick,

    Thank you so much for the explanation, I just have one more inquiry. Could you please tell me what value is 8.32µH, which is given in the description of this coil  WR121210-27M8-ID (8.32µH Wireless Charging Coil Receiver 950 mOhm 0.472" Dia x 0.013" H (12.00mm x 0.32mm)) ?

    Is this Ls' or Ls ?

    Also I do not have to have all the C1, C2, C3, C4, and C5, right ? I can set it up as Cs and Cd according to whatever value I should use. Is that correct ?

    I am looking forward to your reply.

    Thank you very much.

    Best regards,

    Summaiya Siddiqui

  • Summaiya,

    The coil you noted shows to be 8.32uH in the TDK datasheet. This would be the Ls value. Ls' is measured when the coil is on a standard fixture. Generally, on a transmitter is a good approximation. Estimating Ls' from the Ls is difficult since there are many variables.

    Since all of the current produced by the RX goes through the Cs capacitors, we recommend 3. If your current is lower, you may consider less. Since these capacitors are a potential source of heat (based on the power dissipation I*I*R) the ESR of the capacitors is very important. This can be a large source of poor efficiency. Cd is less critical since it is not a current carrying path. A single value can be used if within 10% of the calculated value.

    Regards,

    Dick