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BQ24041: Bad chip / not working properly

FloB
Prodigy 10 points
Part Number: BQ24041

Hello,
we boughts a few thousands of BQ24041DSQR from your online store - so we can exclude a problem of fake / conterfeit chips.

However, approx. 5% of the chips are not working properly, on a stable project where we didn't have any issue before:
- most of the issues is that the battery charging does not start. PG is asserted, but not CHG, even though a mid-charged battery is connected and VIN is within valid range.
- more rarely, the charging current is invalid. For R_ISET = 4.3kohms 1%, we have a charging current of 83mA, which is largely out of spec.

In all cases, just replacing the chip solves the problem, so there is definitely something going on with the chip.

Do you have a known case of bad chips for this reference?

Thanks,
Florent

  • 0
    TI__Mastermind 19195 points

    Hello Florent,

    A few requests first.

    1. Can you attach the schematic for review?
    2. Please provide waveforms showing IN, ISET, OUT, /CHG during startup of the defective boards

    To check whether it is issue with IC you can swap the defective unit's IC onto a known good board (ABA swap). This can tell us whether IC is damaged or not.

    You can also check connections to IC for short/float on the defective boards. 

    Thanks,

    Nick

  • 0 in reply to Nick Brylski
    Prodigy 10 points

    Hello Nick,
    sorry for my mistake, it is actually a BQ24040DSQR.

    Here is our schematic:


    We made the following capture when the BQ is not working.

    Nothing happens. ISET stays at zero.
    CHG = 1.75V
    Vout = 3.65V
    Vin = 5.08V
    ISET = 0.00V

    We made the measures directly at the BQ pins, so it is not a bad contact / soldering issue.

    Interestingly, it is sometimes possible to have the BQ start the charge but it is happening quite rarely upon setting Vin to 5V.
    Here is a capture it if starting sometimes:

    When it works, there is a delay of 35ms between Vin @ 5V and the charge actually starting (ISET is 1.05V and CHG is asserted), which seems expected.
    However, even in this case, the charging current is wrong ; it is 85mA instead of approx. 120mA.
    The BQ does not overcharge the battery, however, and the charge current decreases normally when Vout = 4.185V.

    The slew-rate of Vin seems to be a factor making it work or not. It seems to work almost all the times when the slew-rate is slow.

    Thanks,
    Florent

  • 0 in reply to FloB
    TI__Mastermind 19195 points

    Hello Florent,

    Thanks for attaching the images, the schematic looks ok. Can you also attach the layout?

    FloB said:

    We made the measures directly at the BQ pins, so it is not a bad contact / soldering issue.

    Can you try confirming this by performing the ABA swap? Take a defective units IC and transfer it to a working board.

    Thanks,
    Nick

  • 0 in reply to Nick Brylski
    Prodigy 10 points

    Hello Nick,
    I can't share the full layout publicly, here is the BQ portion:

    However, we tried the defective chips on several good boards, including other projects that have a completely different layout, and the issue is the same.

    Thanks,
    Florent

  • 0 in reply to FloB
    TI__Mastermind 19195 points

    Hello Frorent,

    Will reach out to offline to discuss more.

    Thanks,

    NIck