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Original question:

BQ24630: STAT1 is on without battery connected, but does not charge

BQ24618: Charging issue with Stat1 LED ON

Borx
Prodigy 95 points
Part Number: BQ24618
Other Parts Discussed in Thread: BQ24630,

Hi,

First of all, I have been checking the forums for similar issues, especially on the bq24630 but don't think they are completely similar to my case.

We have been designing chargers based on the bq24618 with no issues. So far we produced a few hundreds that have been operational for a few years (CHGV6).

Now we started designing a version with USB C and tried to increase the power to 5A. To do so, we had an iteration (V8) where we tested both 2xGaN and newer MOSFETs in parallel to test their efficiency (only testing either GaN or MOSFETs). You can also see attached the V8 schematic.

Wrt GaN we followed some recommendations that we have seen from different webinars as GaN have different driver requisites. When we tested the GaN option we suddenly started seeing the issue where STAT1 LED turned on without the battery being connected and we blamed it to some incompatibility issues with driving them.

Then we removed the GaN and added the MOSFETs as seen on CHGV8 production schematics. Everything has been working fine for months, charging batteries without issues. However, last week they suddenly started having the same issues, where STAT1 turns on with no battery connected. We checked waveforms on PH, HDRV, LDRV, REGN and BSTS, attached too.

I replaced the BQ24618 chip on one of the failing chargers and then it worked fine again. Waveforms look good and almost identically as CHGV6. My feeling is that even though we do not connect the GaN Fets, the PH area could be too big in the layout and could mess something up after some time. To me it looks like a layout issue that could damage the bq24618 somehow but would like to confirm that there are no other issues on the schematics (regarding the CHGV8 production variant).

Thanks for your help

CHG versions.rar

0218.Waveforms.rar

PH layout.rar

  • 0
    TI__Mastermind 40705 points

    Hello,

    I would need the full layout to make further comments on the layout

    For the schematic, we typically only use one HSFET and one LSFET. In addition, the combined input capacitance of the 2 GAN FETs are about 5 times larger than the recommended FETs in our datasheet.

    Regards,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    Prodigy 95 points

    Thanks Michael for the fast answer.

    I am adding the Gerber layers here in case it helps. If not, can I send you the full layout privately?

    I wonder regarding the capacitance. It is true that even the new MOSFETs (STL56N3LLH5) have higher capacitance than the originals in the EV kit but they have also lower Total Gate Charge. The same applies to the GaN. That is something that confuses me. Anyway, we are only considering the new MOSFETs option as seen in CHGV8 production schematics where all GaNs and driving circuit is disconnected.

    I calculated the FOM, and both new MOSFETs and GaNs have lower values than the recommended. That is why we chose to replace the FETs, to improve efficiency.

    3247.Gerber.rar

  • 0 in reply to Borx
    TI__Mastermind 40705 points

    Hello,

    I will need the silkscreen as well to evaluate the layout.

    If all that is different is the FETs we need to examine the switching waveforms over 3-5 periods, in particular HIDRV (and actual gate of HS), LODRV (and actual gate of LS), PH, BTST etc. during normal switching operation. Specifically we need to compare the old design to the new design. This does not seem to be an issue with the charger but rather an application issue as the old design works fine but the new one has some issues.

    Regards,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    Prodigy 95 points

    Hei Michael,

    I just added the switching waveforms. I see that the main difference is when no load is applied. It looks quite noise in that scenario and I also remember that I saw this issue when no battery was connected.

    Charger waveforms.rar

    I am also sending you the full Gerber files

    6428.Gerber.rar

    It looks to me like some issue on the BSTS circuit, do you agree?

  • 0 in reply to Borx
    TI__Mastermind 40705 points

    Hello,

    The behavior you sent for the CHG-V8 no load is more of what I would expect than CHG-V6 no load. In CHG-V8 no load we see the part in nonsynchronous mode. CHG-V8 load looked normal as well as CHG-V6 load.

    To fully examine the layout I will need the reference designators for the components. I think what was sent just had the placement overlay for the bottom layer. Maybe the assembly file so I can see which parts are which? From what I can tell it looks like REGN is loaded for the BTST circuit before the capacitor that helps serve as a bypass capacitor for it. The REGN capacitor needs to be as close to the pin, and only connect components after that connection.

    Regards,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    Prodigy 95 points

    Hei Michael,

    Thanks for looking deeper into it. Here I send you the assembly file. I still wonder if the input capacitance could have something to do? When designing the V8 I was looking mainly into the gate charge instead.

    Assembly CHGV8.pdf

  • +1 in reply to Borx
    TI__Mastermind 40705 points

    Hello,

    It looks like the REGN capacitor is indeed loaded by the BTST circuit before the decoupling capacitor. The same is true for the VREF capacitor. The current needs to travel from the IC pin (VREF or REGN) to the decoupling capacitor and then to the other required circuits. (Layout Guideline 9)

    The current sense resistor R8 can be placed closer to the inductor output terminal. (Layout Guideline 4)

    The output capacitor(s) should be placed as close as possible to the sense resistor (Layout Guideline 5). Looks like L7 is closer than C10.

    If using the system rail you need to route the output capacitor ground connections to the input capacitor ground before connecting to system ground. (Layout Guideline 6)

    It looks like the CHGV8 Production MOSFETs are roughly 2x input capacitance, which may have some effect.

    Maybe try to make the layout improvements, the biggest one that sticks out to me is loading REGN before the decoupling capacitor. Seeing as there is no issue with the CHGV6 it is likely related to the MOSFET selection.

    Regards,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    Prodigy 95 points

    Hei Michael,

    Thanks for the answer. In that case we most likely will come back to the recommended MOSFETs to play it safe.

    Thank you for your help.

  • 0 in reply to Borx
    TI__Mastermind 40705 points

    Hello,

    For better performance I would definitely recommend making the layout changes as well, especially the REGN circuit as this could affect the gate drive.

    Regards,

    Mike Emanuel

  • 0 in reply to Michael Emanuel35
    Prodigy 95 points

    Hei,

    Will definetely do.

    Thanks