• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 910 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ51050B: WPC Rx debug options

Pete T
Prodigy 20 points
Part Number: BQ51050B

Hello,

I'm using the BG51050 receiver with a Vishay IWAS3827ECEB100J50 receive coil.  Using the equations for the inductor coil tuning caps I calculated 237nF in line and 2.39nF across AC1/2.  I used 2x470nF in series to create 235nF, and 2.2nF and 180pF in parrallel to create 2.38nF.

The bit of my maths I'm not sure of is the use of 10.7uH for both Ls' and Ls, but this is the only datasheet value for the coil.  Also this is the 200kHz value not 100kHz.

That said, I don't think this is the issue. Vrect is reaching 5-6V.  Very occasionally I get the output working for 5-10 seconds (I'm monitoring my battery current draw between it powering the very low current of the system, and its charge current), but generally not at all.  There are comms with the transmitter, but the transmitter generally falls into fault mode.

Could this be an Rfod related issue?  I'm currently testing with 2 COTs charging pucks (Samsung EP-PG920I, and a Belkin F8M747V2).  The TI Tx chips all look to be NRND, are there replacements in line? Is there a Tx eval board which has debug outputs which will give more feedback that could help point me in the right direction to find the cause of my issues?

This is the schematic as it stands:

  • 0
    TI__Guru* 75676 points
    Hello Pete T
    A couple of things to try, I suspect TX is tripping off due to FOD.
    1.) Increase power reported by RX to add more FOD margin, increase R-FOD (R7) from 200 to 300 and decrease ILIM (R8) from 200 to 100.
    2.) Remove R6, not needed at this point
    3.) Reduce loss on input by changing from 2X470nF to parallel capacitors for 235nF. Recommend using X7R for caps, COG / NPO would work also.
  • 0 in reply to Bill Johns
    Prodigy 20 points
    Thanks Bill, apologies for the delay in replying, fitting in among other work too. This has really helped and almost got me where I want to be. I have also managed to retune for a 19mm Wurth 760308101214 with 100nF and 1nF.

    Pushing the size down, I have then tried using a TDK WR111180-49F5-G 12mm coil - but haven't managed to get this going. It tries, but isnt quite making it into charge mode. This comes out at 80nF and 800pF - how precise would the matching need to be to expect it to work? Theoretically 47nF and 33nF (470pF and 330pF) is perfect - but should 100nF and 1nF be expected to work even if not at optimum efficiency?

    Thanks,
    Regards,
    Pete
  • 0 in reply to Pete T
    TI__Guru* 75676 points
    Hello Pete
    The challenge with small coils will be starting the system, digital ping to start is low power. If the coil is small coupling is poor and voltage at RECT pin will not get above UVLO. Tuning can help a little but decreasing coil to coil distance better alignment of coils will help more.
    My rule of thumb, 15mm to 20mm diameter coils will work, 10mm and less will not, 10mm to 15mm is a gray area.