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BQ27742EVM: BQ27742-G1

kavya medandi
Prodigy 170 points
Part Number: BQ27742EVM
Other Parts Discussed in Thread: EV2400

Hi,

I'm currently working on bq27742 shutdown mode. I'm seeing that when shutdown command is given and monitoring value in multimeter, initially I'm getting 500uA without load and later trying to see how much time it takes to enter into shutdown mode. I'm getting 61uA after 15 mins, but that is not constant and varying like 61,180,250 and again repeating. How to get constant current in shutdown mode and not to take too much time. 

Thanks in advance,

Kavya.

  • 0
    TI__Genius 11770 points

    Hello Kavya,

    The oscillating current suggests to me that the gauge may be in shutdown wait rather than the full shutdown mode. This is because the current drawn by the gauge's internal cpu is cyclical like you describe. See this chart:

    Can you confirm that the charger/pack+ connection is being removed as part of your procedure? 

    thanks,

    Alex M.

  • 0 in reply to Alexander Mazany
    Prodigy 170 points

    Hi Alex,

    I'm not removing pack+ connection when trying shutdown mode. The battery is connected to the cell+ and cell- of EVM and shorting j5 jumper in bq27742 EVM, I'm getting cell+ voltage to pack+. From pack+ I'm giving to microcontroller. If I remove pack+ then I won't get voltage to micro controller.

    Thanks in advance,

    Kavya.

  • 0 in reply to kavya medandi
    TI__Genius 11770 points

    Hello Kavya,

    There is no way to fully shutdown without disconnecting the charger. In this case, since you are shorting CELL+ to PACK+, it sees that and refuses to shutdown. The only solution I can think of, is to somehow disconnect PACKP of the gauge from PACK+. One way to do this would be to remove r13 on the EVM. This is a bit of a strange use-case because normally you wouldn't want the battery to be powering things while the gauge is off, otherwise it cannot gauge properly. 

    I may have misunderstood your system, so please feel free to follow up if you have more questions.

    thanks,

    Alex M.

  • 0 in reply to Alexander Mazany
    Prodigy 170 points

    Hi Alex,

    Thank u for your reply, but I'm not attaching connecting charger to pack+. I'm connecting load i.e microcontroller circuit to pack+. Charger is not connected. Load(microcontroller) is connected. I'm measuring current near cell+ with multimeter. I'm getting fluctuations in current after sending shutdown command. It seems that it is not entering to complete shutdown mode.

    Can you tell me how I can achieve shutdown mode in EVM. Which can I see to verify the state. And are there any hardware points on EVM to check that.

    NOTE:

    No charger is connected at pack+. Connecting controller as load to pack+. I cannot remove load from pack+.

  • 0 in reply to kavya medandi
    TI__Genius 11770 points

    Hello Kavya,

    I tried re-creating this on a similar (but not exactly the same) EVM. As for my previous post, I should not have called it the charger. What I meant is that if cell+ is shorted to pack+, the gauge won't be able to fully shutdown because there is a voltage on pack+ that will keep it on. I referred to this as a charger, even though there is technically no charger. I just said this because it is how the TRM refers to the condition. 

    I'm getting a little confused as to what exactly the setup is here, but have some suggestions.

    1. Check the REG25 pin to see if it is fully shutdown. If it reads 2.5V, the device is still in shutdown wait rather than full shutdown. This is because the LDO only turns off in analog shutdown.
    2. Try disabling comms / removing ev2400. I saw the same oscillating current when the ev2400 was plugged in, but it dropped to a steady <200nA when I unplugged the ev2400. The reason for this is that the ev2400 is constantly sending signals to try and detect the device which pulls power from the gauge via the pullups. 
    3. Ensure the packp pin of the gauge sees no voltage. I see that the MCU is the load and needs to be on, so you may need to find a way to separate packp from PACK+. But if there is any voltage on packp, you cannot fully shutdown.

    Let me know if these don't work for you. I'm fairly hopeful that they will because I saw similar behavior on my setup and doing these helped for me.

    thanks,

    Alex M.

  • 0 in reply to kavya medandi
    Prodigy 170 points

    Hi Alex,

    Sorry for late response. I tried by removing r13 to enter into fully shutdown mode. I shorted CELL+,PACK+ via J5 jumper. I want to know, whether is there any thing if we remove r13 the I2C gets NACK from PMIC for any command sent via I2C.

    Thanks in advance,

    Kavya.

  • 0 in reply to kavya medandi
    TI__Genius 11770 points

    Hello Kavya,

    Packp still needs power when the gauge is on in order to work properly. By removing R13, you can decouple Packp from PACK+, but you will still need to come up with a way to power Packp while the gauge is meant to be on. That will require some extra circuitry and possibly host control. I think a better solution may be to directly tie the MCU to CELL+ and keep PACK+ separated from CELL+. The downside to this is that you would be bypassing the gauge/protection, but you are already doing that via the jumper anyways. It will have some drawbacks on gauging, but if the current is small enough it will be minor. Let me know if this is feasible for you.

    thanks,

    Alex M.

  • 0 in reply to Alexander Mazany
    Prodigy 170 points

    Hi Alex,

    By removing r13 it is entering into the analog shutdown mode. Is there any way to get back to normal mode/ shutdown wait mode by keeping r13 removed.

    Thanks in advance,

    Kavya.

  • 0 in reply to Alexander Mazany
    Prodigy 170 points

    Hi Alex, 

    If there is no possibility to remove connection between cell+,pack+. How to achieve shutdown mode. I tried by removing r13 and connecting gpio pin of controller to packp of ic for voltage to that pin. When I made pin high, so that voltage is supplied to pack. I'm getting normal mode in pmic. When I made pin low,  I'm able to get shutdown  mode only after removing and connecting battery back. When I tried to toggle gpio pin for packp pin with large delay. I'm seeing that pmic is in constant normal mode. It is not going to shutdown mode. How can I make the shutdown possible with this kind of scenario. If shutdown happened, then how to wake up with connecting charger. 

    Thanks in advance, 

    Kavya. 

  • 0 in reply to kavya medandi
    TI__Genius 11770 points

    Hello Kavya,

    I don't see why the solution you laid out here wouldn't work. The only condition I can think of that would cause this issue is the condition that sends "shutdown wait" mode back to "normal" mode if a fault is detected. Maybe removing and connecting the battery caused a POR that cleared the fault? If you read safetystatus() before sending the shutdown command, do you see any faults? 

    In addition, you should be able to wake the gauge up by toggling packp high again via the GPIO. This should appear to the gauge as "connecting the charger". Is that not happening?

    Lastly, how are you verifying the state of the gauge? I recommend measuring the voltage on REG25 to see if it is shutdown or not.

    thanks,

    Alex M.

  • 0 in reply to Alexander Mazany
    Prodigy 170 points

    Hi Alex, 

    I'm verifying the state of the gauge by REG25 only. When I am toggling gpio pin, and measuring reg25 pin it is constantly giving me 2.5v,chg and dschg also giving voltages. That means it didn't went to shutdown mode. I didn't check safetystatus(). I will check it once. And can u tell me what prot checksum is for. And can I match it's checksum.

    Thanks in advance,

    Kavya. 

  • 0 in reply to kavya medandi
    TI__Genius 11770 points

    Hello Kavya,

    See section 4.1.1.18 of the TRM for a good description of the function. Basically the checksum is a backup to ensure there are no errors when you change protector related values, otherwise the gauge could end up false triggering or missing events. It isn't necessary for you to use the checksum to read the faults, so it should not be a problem here. 

    Thanks,

    Alex M.