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bq51013B: Using bq51013B with a Battery Charger that has Dynamic Power Management on the Input

Brian Wengreen
Prodigy 70 points
Part Number: BQ51013B

Hello,

I am prototyping a wireless power system that uses the BQ51013B receiver IC.  This receiver IC provides power to a battery charger that has dynamic power management functionality.  As a result, the battery charger will automatically tune the battery charge current based on the available power on the input (i.e. available power from the BQ51013B).  Sometimes when we power on our wireless power system, the battery charger will set the charge current to 700mA and the output of the BQ51013B will be 4.75V (which meets our requirements) but other times we will see the battery charger set the charge current to 400mA and the BQ51013B will be  at 4.45V (in this case the charge current doesn't meet our product requirements).  In the latter case, the BQ51013B is clearly not providing sufficient power to our battery charger IC.

Our theory is that during the handshaking sequence when the BQ51013B initializes the power contract with the wireless power transmitter, it sometimes locks into a lower power mode and we only get 400mA of charge current.  Can you provide any ideas on how to ensure that the BQ51013B initializes into a higher value power contract with the transmitter?  Since we are getting intermittent results, it seems that the control loop is right on the edge between initializing at a higher power state versus the lower power state. 

Thanks,

Brian

  • 0
    TI__Guru* 75656 points
    Hello
    This may be caused by communications current limit which will reduce output current limit during comm time. This feature can be disabled using EN 1 and 2 pins, EN1=0 and EN2=1.
    The bq51013B will identify itself as a 5W unit, it has no other mode or option.
  • 0 in reply to Bill Johns
    Prodigy 70 points

    Thanks for the response Bill.  We will give this a try.  If we have no power available until the bq51013B OUT comes up on the receiver side, how do we pull EN2 high?  Does it work to just tie EN2 to the OUT pin?  

  • 0 in reply to Brian Wengreen
    TI__Guru* 75656 points

    Hi Brian

    The voltage at RECT pin can be used to pull up EN2.  It will need a resistor & zener diode combination to limit voltage.  RECT is unregulated voltage and can get up to 15V.  The EVM will use a 1k resistor, 5.1V zener BZT52C5V1T-7, and 1uF filter capacitor.