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BQ51013B: Charge pad detection while the RX output is disabled

Amin Rahmati
Prodigy 80 points
Part Number: BQ51013B

Hello TI support team,

I am designing a device with BQ51013B and I need to cut the power after battery become fully charged. I know having EN1=EN2=1 for some charge pads doesn't work and still I might get the power. I can try playing with TS/CTRL pin as well to cut the output power (if this assumption is correct). but my question is in case I could disable the RX output while the device is on charge pad, how can I detect if the device still remains on the charge pad to activate the RX after the battery gets to some low level like 90-95%?

Thank you,

Amin.

  • 0
    TI__Guru* 75656 points

    Hi Amin

    A "charge pad" detection circuit could be built unit RECT voltage as an input.  If unit is on a charging pad the TX is probably pinging RX and RECT voltage will spike up to over 2.7V at about a 5 sec rate.

  • 0 in reply to Bill Johns
    Prodigy 80 points

    Hi Bill,

    Thank you for your support.

    I tried both EN pins and also AD pin solutions. in both cases I can confirm that the output goes to zero while I can detect the charge pad with looking into RECT. but after having the pins back to normal (enabling the circuit) the circuit does not start for delivering power again in some charge pads. I know this is not about RX and it is more related to TX, but why that exact TX re-delivers power to my cellphone after battery drops to some level.

    Is there a way to reset the RX (BQ51013B) to bring it back to normal or is there any other RX IC you recommend to use instead?

    Best Regards,

    Amin Rahmati.

  • 0 in reply to Amin Rahmati
    TI__Guru* 75656 points

    Hi Amin

    This is the behavior of TX and how it restarts after charge complete.  The TX is probably sending a low power ping and measuring the amplitude or decay of the ping then using it to determine if RX has been replaced or moved.  After this the TX will send digital ping and restart a charge cycle.

    As a test try slightly repositioning the RX and see if it restarts.  If this works we have an external circuit that may work.

    Sorry we do not have other RX to recommend.

  • 0 in reply to Bill Johns
    Prodigy 80 points

    Hi Bill,

    I think this is what you explained and it is because of the low power signal from TX although my TX is complied with WPC V1.2.3 and I checked it in WPC website.

    May I ask you please for the external circuit and know how it works?

    Also do you think is there anything (a change in tuning circuit, FOD or etc) I can do in RX side to capture that low power signal?

    Best Regards,

    Amin Rahmati.

  • 0 in reply to Amin Rahmati
    TI__Guru* 75656 points

    Hi Amin

    I will contact you and we can work this question off line.