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BQ25120A: Only seeing 0.5v-1v out

YZ
Prodigy 241 points
Part Number: BQ25120A

Hi,

We have laid out the BQ25120A per "layout example" in the datasheet. In that example, PGND is actually not connected to GND which I think is a datasheet mistake since the description of the PGND pin states that it should be connected to ground (see image below). 

We then corrected this on the PCB with a wire to ground. As soon as we did this the BQ25120A stopped working. If we remove our fix the BQ25120A doesn't come back to life. It only generates between 0.5v-1v. See image below.

Any idea what might be going on?

Signals we currently see. Running on USB only. We see the same behavior when a battery is present as well.

Our layout... PGND to GND was added after PCB was made.

From Datasheet:

  • 0
    TI__Genius 12485 points
    Yuri,

    I think i got the same image posted twice but I know what you are referring to. Both the GNDs need to be tied off at some point for sure. We show them as separate as many applications have more than one ground and they like to isolate the PGND and AGND to prevent noise issues.

    I glanced through your schematic and looks okay. How is the new GND connected? Are there options to connect to multiple locations?

    Have you tried placing VBAT only power? When you refer to the BQ25120A stopped working, are you referring to I2C fail?

    regards,
    Gautham
  • 0
    Prodigy 241 points

    This is the suggested layout from the datasheet (not sure why it didn't show up in the initial post)

  • 0 in reply to YZ
    TI__Genius 12485 points
    Yes. Definitely.
  • 0 in reply to Gautham
    Prodigy 241 points

    Gautham,

    To clarify. When we say stopped working it means it no longer generates 1.8v output. It generates about 0.7v.

    We connected PGND to the same trace as the GND pin

    The same happens when only a battery is attached. (see image below).. The values the BQ generates are lower. With the battery what should be 1.8V ends up being 0.36v where is with USB power it is 0.7V. 

  • 0 in reply to YZ
    TI__Genius 12485 points
    Yuri,

    Since i would be needing deeper information from you, I will send you an email and we can have a discussion there.

    thanks,
    Gautham
  • 0 in reply to Gautham
    TI__Genius 12485 points
    Yuri,

    Since the PGND and GND are not connected, that could be causing the issue. I am closing this post but you have my email.

    Once the rework is complete, please post a new thread or feel free to contact me directly.

    regards,
    gautham