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BQ25150: Problem with buzzing capacitor on PMID pin

Part Number: BQ25150

Hey guys, 

We have recently designed a custom board that incorporated the BQ25150 chip. Now that we have received our first prototype of the board, we realized that the PMID capacitor was producing a buzzing sound which seems very unusual. The capacitor being used on the PMID pin is a 10uF capacitor rated at 25V as recommended by the datasheet. The buzzing sound is not persistent, when we provide Vin, it usually starts off without any problem but then it appears randomly at some point, we were not able to completely narrow down the instance at which the buzzing sound starts. I have provided the schematic for the part of the chip, ignore the 22uF chip at the PMID pin, it was later replaced. Also, something to note is that the 4.7uF cap at the IN pin is only rated at 10V. Could anyone provide any insights into this problem? Any help would be appreciated. Feel free to ask for more information.

  • Hi Sethu,

    Thanks for sharing the schematic I see a problem in your design- the VDD is not meant to be floating. A cap on VDD is required for proper operation. 

    Regards,

    Gautham

  • Thank you, Gautham! I Will make that change and hopefully, it resolves our issue.

  • Hi Sethu,

    Great! I also have few other recommendations. 

    On the audible noise- can you plot PMID to check the voltage and frequency of the noise? I really think the noise issue should go away when the capacitor is not flexed/ contracted due to change in voltage. Placement of the cap on the PCB can greatly impact this. You could cut slots to minimize this effect but I don't think it is necessary here.  

    Schematic: 

    1. /LP pin is not connected. To talk to the device on Battery only mode, you will need the /LP pin to be connected to your MCU as it needs to be pulled high.

    2.  SDA and SCL to be puled up to VIO

    3. Cannot see where PMIC_MR is connected to- is it going to a button?

    Regards,

    Gautham