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BQ51050B: How to detect if the device is still on the charging dock after charging is complete?

Marc GEORGIN
Prodigy 40 points
Part Number: BQ51050B

Tool/software:

Hi everyone,

I'm using the BQ51050B wireless power receiver in my project. The CHG pin is connected to my microcontroller and I use it to detect when charging is in progress.

My goal is to blink an LED during charging, keep it solid when charging is complete, and turn it off when the device is removed from the charging dock.

However, the CHG pin only indicates when charging is happening — once the battery is full, it goes high impedance. At that point, I can't tell whether the device is still on the charging pad or has been removed.

Is there any way to determine if the device is still on the charging dock after charging is complete?

Thanks in advance for your help!

Marc

  • 0
    TI__Guru* 75776 points

    Hi Marc

    Marc GEORGIN said:
    Is there any way to determine if the device is still on the charging dock after charging is complete?

    Yes, The Transmitter will ping the receiver to determine if it is still on the charging pad.  The ping can be seen on the RECT pin as a sawtooth waveform of low amplitude.  This could be used by the MCU to indicate it is still on charging pad.

  • 0 in reply to Bill Johns
    Prodigy 40 points

    Thanks, I have a spare analog I'll try this tips.

    regards

  • 0
    Prodigy 40 points

    Hi again,

    Following the advice I got here, I checked the RECT pin on the BQ51050B, and it does indeed help — I can now detect when the device is still on the charging pad even after charging is complete. When the charge is done, I see a sawtooth waveform on the RECT pin, which is great to confirm the device is still on the dock.

    However, I noticed that the same sawtooth signal appears when the device is not properly aligned on the charging pad (i.e., it's present but not charging due to bad positioning).

    This makes it hard to tell the difference between:

    - A device that is well positioned and fully charged, and

    - A device that is misaligned and not charging at all

    Is there any way to distinguish these two cases using the RECT pin or some other method ?

  • +1 in reply to Marc GEORGIN
    TI__Guru* 75776 points

    Hi Marc

    Marc GEORGIN said:
    Is there any way to distinguish these two cases using the RECT pin or some other method ?

    Do not have a good way to distinguish between the two conditions.  The sawtooth waveform is from low amplitude ping, hard to predict the amplitude.  The TX will also send a digital ping, longer and higher power and increase amplitude above 2.7V to start the RX.