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BQ51050B: Detecting presence of power transmitter after getting fully charged?

tlongeri
Prodigy 70 points
Part Number: BQ51050B
Other Parts Discussed in Thread: BQ51020

I would like to be able to know whether a power transmitter has been detected. Although the CHG pin tells me whether I am currently charging, I want to distinguish between being in charging station and fully charged and not in charging station. I can see no way to do this, but I'm hoping to be missing something. Is this at all possible using the BQ51050B?

  • 0
    TI__Guru* 75676 points

    Hello

    The BQ51050B does not have a Pad Detect feature that will indicate unit is on charging pad.

    It may be possible to look at voltage at RECT pin to determine if unit is on a charging pad.  The TX will ping the charging pad to check for RX and the voltage can be seen on RECT pin.

  • 0 in reply to Bill Johns
    Prodigy 70 points

    Hello,

    Thank you for the prompt response. I have two follow-up questions.

    Does there exist a similar TI chip that does have a Pad Detect feature?

    I imagine pings from TX are rather small in duration and magnitude. I am mostly wondering whether I would have to use an ADC / amplify the signal and whether I'd be looking for a stable output or (probably somewhat rectified) pulses. I understand this depends on the charging pad, but would you happen to know what to expect typically?

  • 0 in reply to tlongeri
    TI__Guru* 75676 points

    Hello

    The BQ51020 / 21 have a Pad Detect (/PD_DET) feature.

    The circuit will capture the ping from TX store the energy in a capacitor then use a compairator to monitor capacitor voltage, /PD_DET is set accordingly.

  • 0 in reply to Bill Johns
    Prodigy 70 points

    I think I will stick with the BQ51050 since I do want the battery charging features.

    It seems like using a comparator (or, more likely, a voltage divider followed by an MCU's comparator) is a fairly simple solution. I will have to do some testing to determine the appropriate thresholds and possibly resistor values, but I think I will be fine with this information.

    Thank you again,

    Tomás