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BQ51221 Heat up when using

Other Parts Discussed in Thread: BQ51221

Hi

I have a problem with BQ51221 on my board, it is going to be warry worm, and do not give much power out.

The construction is similar to application.

I have tried with different coil and it do not change the heating. 

sluuax6b.5287.wireless charge.pdf

  • Henrik,

    Can you tell which part of the board is getting warm?  The coil, IC and  Cs capacitors (C1405, C1412 and C1413) are the usual areas of heat.  The Cs capacitors should be high quality capacitors with a rating of 25V or more.  X7R is preferred since they take all the current through the system.  What is the resistance of the coils?

    I don't see any obvious sources of heat, but do have some suggestions.

    The datasheet recommends to ground SCL and SDA if not used.  It seems the schematic shows them floating.

    Change WP to float (remove R1423.

    Add a 10k resistor to the TS pin (1426)

    Can you leave the OUT pin unloaded without heating?

    Try adding 50 Ohms to the output and measure:  RECT voltage, OUT voltage and OUT current.  Oscilloscope plots on RECT and OUT can be very informative.

    Regards,

    Dick

  • Thanks Dick

    After some check I can see there is used X5R cap.

    I2C is connected to controller,

    What is possible to read on I2C bus on the component.

    I will try to get a FLIR camera to see where it is heating is.

    I will try add 10K at R1426

    Picture of top layer.

  • Henrik,

    The bq51221 register map is in the datasheet section 9.5.

    Regards,

    Dick
  • Hi Dick
    I bought TI EVK and used the coil from this kit on my design.
    This results in that the chip gets hot about 65 C.
    With my own coil becomes about 53 C, but the coil is 72 C.