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BQ51050B: No Charging - RECT Appears Too Low

James Hook1
Prodigy 80 points
Part Number: BQ51050B

Hi,

I am working on a design that uses the BQ5105B to charge a LiPo battery, the design needs to be compact so I'm using a Wurth 760308101219 11.8uH coil (15mm diameter). The circuit is below:

I have the bq51050BEVM-754 and it charges the battery with my Tx so I know that part is ok.

This is what I'm seeing at AC1 and AC2:

And this is what I'm seeing at RECT:

Any ideas are greatly appreciated.

Thanks in advance.

Jim

  • 0
    TI__Guru* 75906 points

    Hello Jim

    It looks like the voltage at RECT is above UVLO (2.7V) and unit does on start and reply to TX. Suspect the gain of system is low.

    Couple of things to try:

    1.) Test with the EVM coil, 40mm X 30mm, if it can work with that one verify the circuit.

    2.) The 15mm coil will have low coupling with TX coil, larger coils improve performance 20mm or 25mm are better. With smaller coil higher L value will help

    3.) Turning the Series resonate caps may help.  Another thing to try is reducing coil to coil distance.

  • 0 in reply to Bill Johns
    Prodigy 80 points

    Thanks Bill - the CHG LED comes on with the EVM coil but it seems to be taking a long time to charge so I'll revisit my R and C values, I have ordered a bigger coil that fits the size I need and will continue tuning.

    Jim