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BQ24105: Heating issues

Prodigy 130 points

Replies: 11

Views: 79

Part Number: BQ24105

Hi.

I'm using BQ24105 as a 3S LiPo charger in one of my projects. The problem is that the IC and inductor are heating. At 0.7A charging current, the IC and inductor are at about 40-50 degrees C. At 1.3A charging current, the IC is untouchable.

Is this behavior normal? If no, what could be the cause? Is it possible to be because of too much heat when soldering with the hot air station (I'm still learning to use this one)?

Attached is the .zip file with the PDF schematic and EAGLE files.

Thanks.bq24105_charger.zip

11 Replies

  • Guru 87590 points

    Hi Ion,

    This is not normal.  I am unable to install the EAGLE software so I cannot review your layout. Can you print each layer in pdf?  Is the IC powerpad connected through vias to an unbroken ground plane that is much larger than the pad itself?  If not then the IC may not have proper heat sinking.

    Regards,

    Jeff

    Please click "This resolved my issue" button if this post answers your question.

     

  • In reply to Jeff F:

    Hi Jeff,

    Yes, the powerpad is connected to the bottom layer. The board size is 26*21mm.

    Uploaded the top and bottom layer. The board is double layer.

    Thanks.

    bq24105_bottom.pdfbq24105_top.pdf

  • Guru 87590 points

    In reply to Ion Popa:

    Hi Ion,

    Thanks.  The grounding looks okay.  Is your board 2oz copper? 

    The return path from the input capacitors to PGND pins is not ideal due to the digital pin traces on the bottom layer, as shown below.  Can you send take measurements of V(IN), V(BAT) to GND at the chip and also I(IN) and I(BAT) so we can confirm efficiency?  Also, can you take a scope shot of the SW node, showing the square wave?

    Regards,

    Jeff

    Please click "This resolved my issue" button if this post answers your question.

     

  • In reply to Jeff F:

    Hi Jeff,

    The board is 1oz copper.

    Tomorrow I will have the measurement tools and will send you the results.

    Also, I will try to assembly one more board with another IC and check if the first IC wasn't overheated during soldering.

    Thanks.

  • In reply to Ion Popa:

    Hi Jeff,

    Here are the measurements:

    Iset1: ~0.666A

    V[in]: 15.00V

    I[in]: 0.568A

    V[bat]: 11.12V

    I[bat]: 0.649A

    Power supply used: Aim-TTi EL302R Linear lab power supply.

    Attached are 2 screenshots made with Rigol DS1054Z oscilloscope on L1 pin 1 (from schematic).

    Are these results expected?

    Thanks.

  • Guru 87590 points

    In reply to Ion Popa:

    Hi Ion,

    The overshoot and undershoot are not expected.  Is your scope probe ground connection large/long or are you using a ground spring like shown below?  

    If not spring and long ground connection, you may be picking up switching noise.  If not, then the undershoot is enough to damage the IC. 

    If you replace the IC with a new one, do you get the same results?  What is the top marking of your IC?

    Regards,

    Jeff

    Please click "This resolved my issue" button if this post answers your question.

     

  • In reply to Jeff F:

    Hi Jeff,

    Unfortunately I cannot find the spring for the probe.

    The measurements in the previous post were done with some wires on both - positive and ground side (bad measurement).

    I redid the measurement again (screenshot)  with the ground hooked to a very small wire with the crocodile clip. The positive side was touching the inductor pad directly.

    I've assembled another PCB and have the same behavior.

    The top marking of the IC is CIF / TI 84J / PENV .

    Is it a problem if I have a 16V Zener instead of 18V (as per datasheet)? On the EVM, the D1 is not present.

  • Guru 87590 points

    In reply to Ion Popa:

    Hi Ion,

    I would not expect a lower voltage zener to cause an issue. 

    Regards,

    Jeff

    Please click "This resolved my issue" button if this post answers your question.

     

  • Guru 87590 points

    In reply to Jeff F:

    Hi Ion,

    Do you have a BQ24105EVM onto which you can install one of the overheating ICs?  This would confirm whether the problem is IC related.

    Regards,

    Jeff

    Please click "This resolved my issue" button if this post answers your question.

     

  • In reply to Jeff F:

    Hi Jeff,

    Unfortunately, I don't have an EVM. 

    I've made another measurement and charged a 3S battery with 1A charge current and got 75% efficiency, which is very low. The IC temperature was ~65 degrees C, which is still well beyond the maximum temperature, but I still think there is a problem with my IC/board/setup.

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