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Development of a non Qi compliant wpt system

Sebastian Heinrich
Prodigy 20 points
Other Parts Discussed in Thread: BQ51013B, BQ51013BEVM-764, BQ500211, BQ51003

Dear sir or madam,

I want to develop a system to transfer wireless power. I want to use the wp-receiver as a constant power supply for a sensor. I won't charge a battery or anything like that. The receiver should be a voltage source. It is not important to me, that the application is Qi compliant. I'dont care about that. I've found the following reference design: http://www.ti.com/lit/an/slua705/slua705.pdf

This is more or less exactly what I'm looking for. But I've several Questions.

1.) Question: Is it possible to use ti controllers lik a bq51013B for power supply only? I guess yes.

2.) So I'dont really need the communication. Is it possible to shut down the communication and use the controllers without?

3.) The reference desgin "low power transmitter" (see the link above) uses another coil than usual but with the same value: 6,3 µH. Why is the transmitted power less than 2.5 W? I don't understand it: Nothing changed?!?

4.) Again to the reference design: Can I use a standard receiver like a bq51013bevm-764 together with the low power solution with the bq500211? Will it work just with a lower output current? Or do I have to develop a special receiver?

5.) Würth Elektronik will release some new coils soon. Receiver coil size: 10mm. I'll use them for my application. So can I just use a bq51013b, change the receiving coil, change the resonance capacitors --> so that all together has again a resonant frequency of 100kHz and it will work?

6.) For me it is difficult to understand, when will the communication protocol fail. So what are the minimum/maximum ratings for AC1/AC2 at the receiver side and the minimum/maximum ratings at the transmitter side of the coil that your firmware will still work. How can I figure out that?

7.) Can I use every coil I want as long as I have the correct resonant frequency and a voltage of at least 5V?

You would help me a lot with your answers.

Sincerely yours

Sebastian Heinrich

 

  • 0
    TI__Genius 14890 points

    Sebastian,

    1)  The bq51013B can be used for a 5-V, 1-A power supply.

    2)  The communication is required for several reasons.  First, the receiver (bq51013B) lets the transmitter know that the object disturbing its magnetic field is actually a valid receiver and not a hunk of metal or something.  Communication also is needed for the receiver to tell the transmitter how much power it needs.  Without the communication, the transmitter may not deliver enough power.

    3)  The reference design you've reviewed shows how to set the bq500211 to run if its supply is limited (such as from a USB port).  The physical size of the coil is different than Qi compliant coils and that limits its magnetic field impacting the power transfer.

    4)  Yes, you can use the bq51013B receiver with a low power solution.  There are a couple of items to point out that will help.  Setting up the proper ILIM resistance is critical.  The EVM has an ADJ setting that will allow you to change the ILIM resistance to allow maximum current of 500mA.  If this is not limited and the system tries to draw more than 500mA, which the bq500211 cannot deliver, the output will collapse.  Another not to consider is that the bq51003 is pin-pin with the bq51013B but is configured for 500mA maximum solutions.

    5)  Exactly.  When you get a new coil, you measure the Ls/Ls' as discussed in the datasheet and adjust the resonant capacitors.

    6)  I am not clear on what ratings you're concerned about.  The firmware will allow the receiver to communicate the power requirements to the transmitter and the transmitter, in turn, adjusts its frequency to accommodate the power changes.

    7)  The only limitation on the coil is the magnetic coupling of the transmitter to the receiver. 

    Always, my first recommendation is to debug the receiver solution with a known good transmitter (EVM) and debug the transmitter with a known good receiver.

    It seems you are well on your way.

    Regards,

    Dick

  • 0 in reply to Dick Stacey
    Prodigy 20 points

    Thanks Dick,

    I'll come up with new questions as soon as the need arises.

    Regards,

    Sebastian