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1A load step issue

Sean Can
Prodigy 70 points
Other Parts Discussed in Thread: BQ500210, BQ51013A

Hi,

I am using bq500210 as Tx solution and bq51013A as the Rx solution. I have notices an issue when I try to introduce a 1A step load at the receiver output. The instant I introduce the Rx coil (with 1A load at the Rx output), I see 5W  (5V, 1A) output but after a second or so this goes to 0W (0V, 0A). A few seconds later I see 5W output again but like the previous time it goes to 0 again. I only see this happening when the step change in load is 1A. I dont see this when I gradually increase the load from 0 to 1A  and I also dont see it when I have a step change in load of 0.5A or so. Is it the communication protocol which is the problem here. I have 40nF as the COMM capacitors. Any input in this regard will be helpful.

Kind regards,

Sean

  • 0
    TI__Guru* 75656 points

    Check the input voltage to the TX during the load step and see if it is dropping.  Additional bulk C will help to reduce voltage drop if it is a problem.

    Also note if the AC signal on the coil stops at this time.

     

    Check the V-Rect voltage RX (pin C2 and C3 on CSP package), if this voltage is dropping below 5V this could be a problem.  Additional bulk C at this point will help.

    Increasing RX current limit may help this is set by the resistor on ILIM (pin G1), lower resistor value will increase output current.

     

    Probably not a communications issue, you would need to have problems for longer than 1.2 sec to trigger a shutdown and restart.

  • 0 in reply to Bill Johns
    Prodigy 70 points

    Dear Bill,

    Bulk capacitors at Vrect has helped a bit but now and then it tends to shutdown when i introduce a 1A step. I think I am operating it at the boundary of stability. I will try to find out exactly what part of TX electronics is causing this. Thanks for your comments.

    Regards,

    Sean