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Original question:

BQ51013B: BQ51013B - Problems with initialising

BQ51013B: BQ51013B - Problems with initialising

Andre Iwers62
Prodigy 90 points
Part Number: BQ51013B

Hello There,

I have used this chip successfully on my prototype Boards. However, now I would like to change the coil to a smaller one (same board).

TDK WT202012-15F2-ID
Ls [uH] : 6.20 uH +/- 5% @100kHz
Rs [Ohm] : 0.095 Ω +/-10% @100kHz
Rdc [Ohm] : 0.08 Ω typ

My measured values for the inductor are are 6.40 uH (100kHz) and 6.80 uH (1MHz).

The on the RECT pin is constant at 5-6 V depending on the C1 and C2. C1 I chose to be 330 nF, C2 4nF.

The output does not deliver anything. Any idea what it could be? If I replace the coil with the old one everything works just fine.

Signal on RECT pin:

Kind regards

  • 0
    TI__Guru* 75656 points

    Hello

    The TDK WT202012-15F2 is a small transmitter coil and will work well as a transmitter coil.  But will not work well as a receiver coil, L value too low.

    Take a look at TDK WR222230-26M8-G small receiver coil for your application.

  • 0 in reply to Bill Johns
    Prodigy 90 points

    Hello,

    Thanks for the hint, I forgot about that. However I have another one here: AWCCA-15N15H06-C01-B

    L = 14.6 uH, C1 = 170nF, C2 = 2nF

    Voltage on RECT pin:

    What exactly determines that the device starts? Could it be that the coil can't deliver the current? I set it to be 200 mA. RILIM around 1.3kOhm but did not change the fact that it is not running.

     I would appreciate any further hints.

    Kind regards

  • 0 in reply to Andre Iwers62
    TI__Guru* 75656 points
    Double check the voltage that RECT is increasing to-- it should be 7V, but I think it is only about 5V.

    You see Signal Strength, ID and Config at the start, flat area at start (freq fixed at 176kHz).
    This goes well and unit moves to power transfer phase and the voltage at RECT needs to be increased to 7V.
    The voltage rises under the request of the RX.
    But appears to stop at about 5V---The system may run out of gain.
    Then it sits there the RX is sending packets, possibly asking for more power.
    If the voltage does not increase to 7V target the RX will stop trying (packets stop) and the TX shuts down.
    Is the time from last packet to TX shutting down 1.5S?
  • 0 in reply to Bill Johns
    Prodigy 90 points
    It is 1.2seconds.

    I will order some more coils to see which works better. I will post my outcome as soon as I got them here.
  • 0 in reply to Andre Iwers62
    TI__Guru* 75656 points

    Which TX are you using?

    The other problem could be coil to coil spacing, does getting the coils closer together help?

    Problem with small coils (15mm to 20mm) is poor coupling factor and low gain.

  • 0 in reply to Bill Johns
    Prodigy 90 points
    I got a standard charger platform here (Comsol Qi Wireless Charging Pad White).

    I already took of the cover to put the RX coil straight on top of the TX coil. The voltage never rises above 7V. Maximum is around 5.3 V.

    Kind regards
  • 0 in reply to Andre Iwers62
    TI__Guru* 75656 points
    Something to consider, replace the 50mm TX coil in your charging pad with the 20mm TDK WT202012-15F2-ID TX coil you have.
    Coupling factor between small RX and TX coil is better and you could have improved performance.