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BQ27Z561: gauging only on a none rechargeable battery Li-SOCl2, Lithium Thionyl Chloride

Marien Vermeulen1
Prodigy 230 points
Part Number: BQ27Z561
Other Parts Discussed in Thread: BQ35100, , BQ25100

We want to use the BQ27X561-R2 for an non rechargeable battery of 3.6V / 12 Ah.  (single discharge usage)
We selected the BQ27Z561-R2 as this battery gauge is very low power. We need this spec as we make a low power IoT monitoring system.
it is 99,4% if the  time standby:  20 uA,  and the rest is about 5 mA.   besides this modern device seems very intelligent and complete.
We placed it on our first prototype and are discovering the features and test it.
The  BQ27561-R2 is very clever for rechargeable batteries.

We are evaluating with the help of BQ-studio and the EVM kit.  Very handsom.  The tool includes the chemistry for the  Li-SOCl2 batteries like:  Saft LS17500

We want to:
     read:  current, voltage and temperature:   this works fine
     read: charge: we do this now with:  QMax passed Q, or True Rem Q

We have do have some questions now.
Is it possible to get relative state of capacity ??

Can we use the intelligent features like there are for chargeable batteries?
(like from the Impedance Tracker: correction aginst temperatue and internal resistance)

  • 0
    TI__Mastermind 19195 points

    Hi Marien,

    This gauge is not intended for LTC battery. Please consider using bq35100.

    Thanks,

  • 0 in reply to Nick Brylski
    Prodigy 230 points

    Hi Nick  thanks for this tip.
    I did not evalute this chip for my design.   When I look quickly to the datasheet I see two specs:
    6.3 Recommended Operating Conditions
    6.5 Power Supply Current Static Modes

    The fist reports very low power consumption.  the second rather high.

    With the BQ27Z561 We run normal at 66 uA, and in deep sleep at 9 uA.   this meets our design requirment.
    normal mode is 0.6% operational time,  99.4 % is standby.
    Standby we have te measure 20 uA
    Operational:  0.5 to 30 mA very pulsive. For this the gauge must integrate continuous the current very well.

    I must study the complete datasheet of this BQ25100.
    Can you say is the BQ35100 is low power enough and will integrate de capacity very well? 

  • 0 in reply to Marien Vermeulen1
    Prodigy 230 points

    The BQ35100 should be controlled with the GE input..  So our MCU should activate and deactivate the chip?
    When the we should drive GE always high,  the current consumption is as in 6.5..
    I would expect this chip more clever than i Know by now...

  • 0 in reply to Marien Vermeulen1
    TI__Mastermind 19195 points

    Hi Marien,

    Bq27z561 will not be able to give an RSOC for primary cells, you will need to do the calculation yourself. The deadband current for bq27z561 has 1mA resolution so it would not capture the standby current for your system.

    We strongly recommend switching to bq35100 for this application. 

    Best regards,

  • 0 in reply to Nick Brylski
    Prodigy 230 points

    Hi Nick,  thanks for advise.
    Our application can not drive a GE pin.  We prefere a standalone gas gauge.
    To get a low gas gauge current for this BQ35100,  we must implement the GE pin to the application.
    Before we make plans to this.
    Can you confirm:  that this chip will CC the active current very well is well?
    The active current takes 6 seconds  each hour.  the pattern is from 1 mA to 30 mA, very changing/pulsive in 5 ms intervals.
    The active current shal be about 80% of the battery energy, so must be measured very accurate, to make the gas gause
    a worthfull device.

  • 0 in reply to Marien Vermeulen1
    TI__Mastermind 19195 points

    Hi Marien,

    That current accuracy will be board dependent but the bq35100 can achieve 1mA accuracy. Depending on the size of the sense resistor it could go lower.

    Best regards,