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BQ51020: Wireless Receiver Design Questions

Orlando Sellers
Prodigy 20 points
Part Number: BQ51020
Other Parts Discussed in Thread: BQ51003

Hi you all,

I am a Purdue University Electrical Engineering Student designing a wireless charging circuit with your BQ51020 I had a couple of quick design questions I was wondering if you all could help me out on.

1) The first question is can I disable the Foreign Object Detection (FOD) on the BQ51020. And if not, is there any appropriate value I can set it to that will prevent my device from being disabled by the transmitter on accident. I have a time constraint this semester and I am trying to create a proof of concept prototype. This semester I don't have the time to design a test circuit, and properly calibrate and calculate R_FOD. I am using a TDK 20mm receiver coil with a backplate shielding. L = 11uH and L' was tested to be L' = 12.222uH for the coil. I highly doubt I will have any power absorbed by any other components because my application for the receiver coil require that the coil is far from all other components including the BQ51020 PCB, 12cms or more behind the shielding plate. I found when reading the documentation for FOD calibration that for a typical R_FOD is 495 Ohms. I don't know any of the assumptions made with that statement but will using that value for this state of my product, prevent an FOD error from halting my charging? Or should I scale that number up or down and if so approximately by how much?

The next 2 questions are much simpler and quicker...

2) Can I just pull the "inverse AD_Enable" pin high to disable the adapter plug in setting? I don't need it for my application.

3) What is a typical T_ping value to set the bleed off resistor to, that is parallel to the C_MEM capacitor? I looked through some data sheets and scroll around the internet and I couldn't find anything that quite seemed to be what I was looking for. I want my receiver to be able to communicate with as many if not all Qi transmitters as possible. I currently just have T_ping set to 1 second in the calculation.

Thanks a ton for any assistance, and have a great day you all.

Regards,

Orlando Sellers

  • 0
    TI__Guru* 75486 points

    Hello Orlando

    1.) The FOD cannot be turned off on the BQ51020 ( RX) side.  It will report to the Transmitter (TX) power it has received and this is based on voltage at FOD pin along with output current.  The value of R_FOD can be increased to make it less likely FOD fault will be set.    Also note that a 20mm RX coil is typically lower power about 2.5W .

    2.) Pull "inverse AD_ENABLE" pin high? -- Do not recommend this.  Better option is to ground AD pin this will disable the AD_ENABLE output.

    3.) T_Ping is typically 500ms but will vary from manufacture to manufacture.  Also the amplitude of the ping will vary.  Goal of the T+MEM RC is to keep the voltage above 1.6V when on the pad and TX is sending the low power pings.  Typical value is 5.6M ohms and 2.2uF, but can be increased.

  • 0 in reply to Bill Johns
    Prodigy 20 points

    Hey Bill thanks a ton for the help! And yes my initial design was actually to use the BQ51003 which is a 2.5W solution, however unfortunately due to the shortage TI and all notable distributers are completely out of stock until Fall 2022. 

    Have a great day 

    Orlando