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BQ51050B: Troubleshooting, Circuit seems to communicate with the QI charger but isnt charging the battery.

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Replies: 5

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Part Number: BQ51050B

Hello,

I have developed a pcb for wireless charging of a LiPo battery using the bq51050b IC. My design is based on the reference design. When i put the coil on the charging pad and look at the RECT signal (as this is stated to be the best indicator of the circuit receiving something from the charger) it shows the following:

Im not sure what this means for the system and if it should be working like this or not. The led indicating if the circuit is charging also isn't lighting up. How do i proceed troubleshooting the system and finding out how to get it work?

  • Hello,

    From the waveform, it looks like the TX is pinging the RX, causing VRECT to pulse, but the RX is not communicating back to the TX to engage in and maintain power transfer. Are there any differences at all from the reference design? Could you verify that there are no unwanted open or shorts in the circuit, specially at the COMM and CLAMP pins and caps?
    Also, What TX are you using for your testing? Do you have multiple boards and if so, are all showing the problem or just one?

    Thanks!
    Norelis
  • In reply to Norelis Medina:

    Thank you for making me check the board for shorts again ;-) should have thought of that aswell, there was a short between pin 4 and 5 on the ic. i fixed the issue and now it is charging fine.

    Regards,

    Tim

  • In reply to Tim Kleinloog:

    Excellent! Glad I could help.
  • In reply to Norelis Medina:

    Hello,

    I've copied the TIDA-00329 and used the rx coil 760308101219 from wurth. It seems that I have the same problem : rx ping, but no tx allowed (RECT has a similar behaviour).

    I've checked the short circuits, but there is none. I have a first question : if EN2 is low, and AD is low too, will a wireless charge happen?

    The second question : what should I check to have more precise details? I've set the charging current to 50mA with a 5k resistor, is it too much?

  • In reply to Cedric Decouen:

    When using a small coil we recommend increasing the inductance to offset a lower coupling factor you will have with this type system. The 760308101219 is 15mm (small) coil and L value is about 11.8uH which is OK for a large coil but low for a small coil. Take a look at the coil used in TIDA-00318, it is about 27uH.

    An indication that L is low or tuning is off, look at Voltage a RECT pin it should exceed UVLO of 2.7V.

    Best Regards,

    Bill Johns,  Applications Engineer

    Texas Instruments Inc

    Dallas, Texas

    For more information on Battery Charger Solutions see Link

    Search "FAQ" on E2E Forum for common questions on battery charger solutions. 

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