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BQ51050B: Recharge behaviour

Bart van Hest
Prodigy 10 points
Part Number: BQ51050B
Other Parts Discussed in Thread: BQ51013B, BQ51003

We have an application where the device might stay on the charger for a prolonged time, let's say several days. The customer wishes that the battery stays close to fully charged while the device rests on the charger.

Now, we are seeing different behaviour on different chargers.

On a Zens PUK2 there is an initial charge after which the charging stops and never restarts.

However, on a Trust Qi charger the behaviour is the desired behaviour; a recharge is triggered whenever the battery voltage drops below a treshold:

Both chargers are WPC compliant and since it is the power receiver that controls the power transmitter I would have expected identical behaviour.

Now, what should I expect? The recharge behaviour of the BQ51050BRHLT we are using in a design is not completely clear to me. In the datasheet of the device, the only mention of recharge is under the 'electrical characteristics' section on page 8; a threshold of -135mV..-90mV is mentioned there. In the rest of the datasheet, appnotes or other documentation there is no mention of recharge.

If we want to accomplish recharge behaviour like in the second image on the Zens charger (which happens to be the approved type), what would be the best method to do so? Would controlling the AD pin from software, tricking the BQ51050B in thinking that there is an AC adapter attached, accomplish this?

Best regards,

Bart van Hest

  • 0
    TI__Guru* 75676 points
    Hello Bart van Hest
    The BQ5105XB will use End Power Transfer Charge Complete (EPT01) to control the transmitter when charge is complete. At this point the battery is charged and TX turns off. If the TX pings the RX it will reply with EP01 as the first packet, power transfer will not start.
    When unit has been on the charging pad for some time and voltage has dropped below recharge RX will no longer reply with EPT01 but enter power transfer and restart charge.
    From a TX standpoint what it will do after ETP01 has been received may be the issue. Does it turn off completely and only monitor the charging pad to see if RX is removed. This would be a low power analog ping possibly other method.
    For the RX to reply it will need the TX to send longer higher power digital ping.

    I am not sure of the behavior of the above TX devices they may only use the lower power analog ping to look for RX placed on TX and not send digital ping to check if recharge is needed.

    Some testing can be done using the bq51013B or bq51003 EVM -- pull EN1 and EN2 high to simulate charge complete.

    Toggling AD pin would not help if the TX is not sending digital ping. If the TX is only sending analog ping the amplitude of this ping need to change to detect the RX has moved.