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BQ27742-G1: BQ27742-G1

kavya medandi
Prodigy 170 points
Part Number: BQ27742-G1
Other Parts Discussed in Thread: BQSTUDIO, BQ27742EVM, EV2400

Hi,

I'm currently working on BQ27742, I achieved shutdown mode using this. I wanted to try Full Sleep mode.  I tried different methods as mentioned in reference manual. But, not successful in achieving current as mentioned in datasheet. The methods which I followed are below,

1. Sleep current=15mA, FS wait=0, entered manually into full sleep by giving FULL_SLEEP command.

2. Sleep current=1mA,FS wait=5, tried to see whether Full sleep is achieved automatically.

Not achieved required current. Sometimes, when I used 1st point I achieved full sleep current, but not always. And the current is varying for every second. Not as mentioned in datasheet for every 20secs. And the range of current is 65uA - 300uA for every 2 secs.

How can I achieve Full sleep?

Thanks in advance,

Kavya.

  • 0
    TI__Guru** 102355 points

    Hello Kavya,

    If you set your Sleep Current to 1mA the device may never enter sleep since the current value is in the noise level. I would make sure it's at least above the deadband for any testing.

    There should also be no communication or current after sleep mode is entered, or it will exit sleep mode. If you are using bqStudio make sure you turn off the auto re-fresh functionality.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 170 points

    Hi Wyatt, 

    Thanks for replying. I'm having pmic and msp430 controller on board. Controller acts as load to pmic. I'm performing full sleep before I make controller into lpm3.later controller goes to lpm3 and current observed in lpm state is 25uA for controller. i'm getting 65uA by adding both pmic full sleep and controller lpm. Will this combination effect full sleep current. Above you mentioned no current. What does that mean. Is it total board current? 

    Thanks in advance, 

    Kavya. 

  • 0 in reply to kavya medandi
    TI__Guru** 102355 points

    Hello Kavya,

    I mean the gauge should only be reporting current below the sleep current threshold. 1mA is below the deadband, it would only make sense to set it above the deadband. The conditions outlined in the TRM are most likely still not being met, I would double check to make sure there is no communication and that the current you use to check the gauge mode is the VPWR pin and not the total current of the system.

    It doesn't seem like any of your current values would be large enough for the gauge to measure so I don't believe that would be an issue. Can you share schematics of the design?

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 170 points

    Hi Wyatt,

    I tried to achieve full sleep in bq27742EVM using BQ Studio. I'm sending FULL_SLEEP command from BQ Studio to EVM. I removed I2C lines connection from EV2400 to EVM. I'm seeing the current of 37uA in full sleep. But as mentioned in TRM, after entering into full sleep mode the PMIC should wake up for every 20secs. That means, there must be current variation after 20secs. But I'm seeing current variation for every second( 37uA -250uA  fluctuation). How to achieve scenario of PMIC wake up for every 20secs as mentioned in TRM. 

    Thanks in advance,

    Kavya.

  • 0 in reply to kavya medandi
    TI__Guru** 102355 points

    Hello Kavya,

    You are most likely violating one of the conditions stated in the TRM to enter sleep (section 2.7.2 SLEEP Mode and 2.7.3 FULLSLEEP Mode)

    The gauge uses a comparator to determine if it should wakeup so it will not take much noise on the SRN and SRP pins to wake the gauge.

    You may still see current every 1 second when the gauge wakes to check the watchdog, but there should be a larger pulse every 20 seconds. You should be estimating the power mode using the average current for the period, the gauge will spike well above the datasheet current values while performing MCU calculations.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 170 points

    Hi Wyatt,

    We are able to achieve the full sleep mode and we are still observing current fluctuation in current. So, please find attached video showing fluctuation in current. 

    Ammeter is connected between battery source voltage and CELL+ of EVM.

    Thanks in advance,

    Kavya.

  • 0 in reply to kavya medandi
    TI__Guru** 102355 points

    Hello Kavya,

    The EVM may have other losses associated with it, please measure the current directly into the gauge (VPWR pin) with a scope if possible. The values for the sleep mode currents in the datasheet are based on the average values for the gauge. The current will still pulse.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 10 points

    Hi Wyatt Keller,

    I am colleague of Kavya. She is following up with you but seems she is unable to get proper answer.

    Let me clarify you few things.

    There are no other losses associated with because we have tested it without loading with other circuitry. You can clearly see current is going as low as 35uA.

    You have multiple times specified that fluctuations will be there in full sleep current. So can you tell what is the expected scale of fluctuations?

    If fluctuations are expected, then why it is no where mentioned in datasheet or refrence manual.

    Seems like few things are not clear in datasheet.

    Anyways let us know if you really know the solution to achieve 40uA (average current) in full sleep mode. 

    Since this product is going to be in production very soon. We don't have enough time to discuss over forums multiple times to get solution or atleast clarity.

    So we need a priority support. Can you guide us where to get support on highest priority?

    I hope you understand our situation and won't ask further questions from us.

  • 0 in reply to Fahim Ahmad
    TI__Guru** 102355 points

    Hello Fahim,

    Our data sheet specifies the average current consumption in different power modes, it can sometimes be confusing for customer since the short pulse can be much larger than the "specified" current value. Depending on what operation the gauge is doing the pulse can very. most of the time it is less than a few hundred uA for a very short time.

    From the measurement on the DMM it's not clear for how long the pulses are high in order to take an average measurement. If you have more detailed plot and images/data to show the average current that would be the best way to validate what the true consumption is.

    Sincerely,

    Wyatt Keller