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Original question:

BQ25792: Multipurpose use of QON?

BQ25792: Reset/Ship Mode Issues

Bob Green
Prodigy 40 points

Part Number: BQ25792

We're trying to implement some form of power down on our device using the Ship FET on the BQ25792.   /QON is connected to a momentary switch to ground and one of our controller GPIOs.   The idea was to have the controller detect a short button press then place the charger in ship mode over I2C then have the charger wake up using the same switch on /QON.   When we implemented this I could see that the controller was detecting the button press correctly and got the message that it was writing to the charger to select Ship Mode.   At this point I expected to see the power supplies fed from the Sys Out of the charger to shut down taking the controller with them.   Nothing happened.   As a sanity check, I held the button for 20s verifying that the /QON pin on the chip was low expecting to see a reset.   Again, nothing happened.   I monitored the SDRV out and didn't see any activity when I tried the system reset.    Any other suggestions for debugging this issue?   Out ship FET is an infineon BSC120N03LSGATMA1 with a Vgs(th) similar to the TI FET on the EVM board.   

  • 0
    TI__Guru**** 181076 points

    Hi Bob,

    For ship mode to function, VBUS voltage must be below UVLO (i.e. no adapter present and OTG not enabled).  I assume that was the case?  Also, SDRV can't have a dc resistive load <=50Meg (like a voltage scope probe with 10Meg resistance) or it will not function correctly.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 40 points

    Jeff - Thanks for the quick response.   I didn't have an adapter connected and verified that the voltage at VBUS pins was 0v.   SDRV is connected only to the gate of the ship fet and I made sure to try without any probed connected.   Is it possible to check the SDRV function if I remove the Ship Fet?

  • 0 in reply to Bob Green
    TI__Guru**** 181076 points

    Hi Bob,

    With a regular scope probe on it, the SDRV output should go low correctly but does not reach a high voltage to turn on the NFET due to oscillation . Just to confirm, your ship FET is installed as shown below with SOURCE tied to BAT:

    Also, what is the battery voltage at which you are trying to enter ship mode?  For a 1S battery, the thresholds are a bit high:

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 40 points

    Jeff,   

    Here's our implementation (FET Source on BAT Pin): 

    This is a 4S battery so we're well above the thresholds.  Hopefully you'll see something in the schematic, let me know if you need more details. 

    Thanks, 

    Bob 

  • 0 in reply to Bob Green
    TI__Guru**** 181076 points

    Hi Bob,

    Did you tell the charger that the shipFET is installed by setting REG0x14b7=1 before writing to the ship mode bits?

    Regards,
    Jeff

  • 0 in reply to Jeff F
    Prodigy 40 points

    Hi Jeff,    The FW team just reported that they do not set this bit on config.    Hopefully that will resolve the issue.   Would this affect the reset function as well?   

  • +1 in reply to Bob Green
    TI__Guru**** 181076 points

    Yes.  I think this is your issue.

  • 0 in reply to Jeff F
    Prodigy 40 points

    Jeff - I had the FW team set REG0x14b7=1 in the config, and we still didn't get the correct result.   I also asked them to try setting the REG0x11b0 = 1 to remove the delay.   Again, no luck.    Are there any other config parameters we need to set to make this work correctly?   I'll have another debug session with our FW team this afternoon to go over their config sequence.   Also, any status registers we can ping to see if the SFET status?

  • 0 in reply to Bob Green
    TI__Guru**** 181076 points

    HI Bob,

    I am not aware of any other settings.  I tried on my EVM and ship mode worked when I set only those 2 bits.  There is no SFET status bit other than the ship mode bits themselves.  If ship mode is not allowed for whatever reason, the ship mode bits reset to default. 

    Regards,
    Jeff 

  • 0 in reply to Jeff F
    Prodigy 40 points

    Jeff - Thanks for your help.   It seems that we had a hardware issue on the board I was testing.   So far its working on the second board I tried.