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BQ51013A: Combining with BQ25060 to wirelessly charge Li-ion battery at 1.0A - not achieving max charging current.

Aran Dasan
Prodigy 40 points
Part Number: BQ51013A
Other Parts Discussed in Thread: BQ25060, , BQ51013B

Hello TI forums.

We are using the BQ51013A Qi wirelss power supply receiver IC combined with a BQ25060 Li-ion battery charger IC, as per the following diagram (PDF). We have designed for a 1.0A charging current, but we are only seeing 500mA at the battery.

Charging Circuit.pdf

The Li-ion battery is represented by connector J2. It is a 1S2P 3.7V Li-ion battery pack (two 18650 cells in parallel with integrated BMS with 10k thermistor)

We desire to charge the battery with IOUT = 1.0A. As such, we have made the following design choices:

  • BQ25060: 
    • EN pin pulled down to ground,
    • ISET pin pulled to ground via 1k resistor (R5)
  • BQ51013A:
    • ILIM pin linked to ground via total "RILIM" resistance of 110R + 140R (R4 and R2, respectively) = 250R total. This should set IMAX to 1.0A.
    • We have followed the standard process of measuring the inductance of the RX coil in--situ in the device to derive the correct resonant capacitor values.

Using an Otii Arc battery simulator, I record the current arriving at the battery as follows:

In the above graph, the Y-axis is current in mA, X-axis is time in seconds. Negative current means current entering the battery, ie. charging. The spikes show that the rest of the circuit is drawing current during the charging process occasionally). On average the battery receives 500mA, which is half of the desired charging current of 1000mA.

The Qi transmitter we are using is an off-the-shelf charging pad that should be capable of delivering 10W output. We have tried multiple different charging pads, but we are experiencing the same charging current across all of them.

Please could you review our circuit diagram, to see if we have made any mistakes in our design? Or are there any other factors we have missed and could change to achieve 1.0A charging current?

With kind regards,

Aran

  • 0
    TI__Guru* 75656 points

    Hello Aran

    I have reviewed the schematic and did not see any problems.

    What RX coil are you using?  What is the case thickness, coil to interface surface?

    Is the 5V out of BQ51013A stable, are you possibly seeing drops in the voltage?

    Any reason you are using the BQ51013A?

    The BQ51013A is an older device and has been replaced by the B version, BQ51013B.  The two devices are P2P. 

  • 0 in reply to Bill Johns
    Prodigy 40 points

    Hello Bill, thank you for your reply.

    • RX coil: TDK WR483245-15F5-G (product page)
    • Case thickness: Currently 6mm, but we are observing the same behaviour when we vary this between 1–5mm also.
    • The interface material is acrylic plastic (PMMA), but we are observing this same behaviour across a variety of materials, including a plain air gap
    • Yes, we are indeed planning to replace the BQ51013A with BQ51013B. We started with the BQ51013A due to chip availability, but we have secured a supply of the BQ51013B now for production.

    I've re-taken measurements this morning:

    • I am now recording input power into the battery using the battery simulator, which averages at 2.08W
    • BQ51013A 5V output steadily reads 4.903V using an oscilloscope
    • I've also measured the RECT voltage, which reads 5.00V using an oscilloscope
    • I've attached the schematic for the wider power stage of the circuit, in case it is of help, below.

  • 0 in reply to Aran Dasan
    Prodigy 40 points

    Interestingly, if I cut the BQ51013A out of the circuit, and supply 5V directly to the BQ25060, I still see only 2W, exactly 500mA arriving at the Li-ion battery simulator. This leads me to suspect that the BQ25060 might not be functioning correctly. Could the IC be stuck in USB-500 mode somehow?

  • 0 in reply to Aran Dasan
    Prodigy 40 points

    Last one from me today - Separately, I'm using the BQ25060 EVM evaluation board with a bench power supply set to 5V. I still cannot get a 1.0A charging current to my battery simulator - the most I can get is 2W / 500mA, with EN (JP1) pulled to ground, and ISET set to 1.0A via R6.

  • 0 in reply to Aran Dasan
    TI__Guru* 75656 points

    Hi 

    The coil is a good one, WR483245-15F5G 48mm X 32mm and 13uH

    Case thickness needs a closer look, max Qi coil to coil distance is 5mm.  Problems will be at start up, cannot generate enough voltage to start.  But if you are testing at less that is not the current problem.

    Plastic case will not be a problem.

    Transition to BQ51013B will not be a problem, only change area is the FOD feature to support WPC 1.1 / 1.2.

  • 0 in reply to Aran Dasan
    TI__Guru* 75656 points

    Hi

    The unit should not be in USB-500 if the EN is connected to gnd.  Connections looks OK.  But if pin is floating it will be in USB500 mode, possible bad solder joint or PCB issue?

    Unit has Thermal Regulation, if the device overheats output current will be reduced.  Check thermal pad connection.

  • 0 in reply to Aran Dasan
    TI__Guru* 75656 points

    Hi 

    Could this be a battery simulator set up issue.  A power supply with voltage and current regulation can be used to test the simulator.  Set power supply voltage to 3.6V and adjust current to simulate charger current regulation.