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In BQ series Which Battery gauge chip will be suitable for me ??

Rakesh Muralidharan
Expert 2810 points
Other Parts Discussed in Thread: BQ27510, BQ27500, BQ27010, BQ27210, BQ27510-G2, BQ27501, BQ27505-J4

Hi,

My application uses Nokia E61i (lithium ion) battery with a capacity of 3000mAh.

I am in lookout for a battery gauge chip that can implemented inside the system and not embedded in the battery pack.

I need to determine the residual capacity of the battery. The important point is that I am not online charging the battery in our system , but charge it offline in a remote location and reinsert the recharged battery to the system. i guess Coulomb count technique may not work in this scenario. May be the prediction may not be very precise but an approximate judgment would do.

Can battery gauge chips sense the capacity with a reasonable degree of accuracy in this condition??

Which chip will be suitable for this removable battery pack application??

Thanks in advance for your key inputs.

 

 

 

  • 0
    TI__Genius 14985 points

    Hi Rakesh,

    You can choose from among our system-side Impedance Track gauges like bq27500 or bq27505 (needs external 2.5V LDO for power), bq27510 or bq27520 (integrated LDO).  They are designed for removable batteries.  Even though you will charge the battery outside of the system, when you insert it the gauge will take an OCV (open circuit voltage) reading to establish the starting SOC (state of charge).  Ideally you want to make sure the battery is well-relaxed before inserting it.  That means it's best not to take it off the charger in the middle of a charge and pop it right in the system since the battery voltage will be slightly inflated from the true relaxed OCV voltage.  However, if you do this the error won't be that bad, and it will correct itself when you system allows the battery to relax enough to take another OCV reading.

     

    You could also use a coulomb counting gauge like bq27010 or bq27210, but as you already realized you will need to make sure the battery is already full when you insert it and then initialize the gauge to know that the battery is full.

  • 0 in reply to dMax
    Expert 2810 points

    Does that mean that if we insert a partially charged battery  then the capacity predictions would be erroneous??

    Is the prediction algorithm battery technology dependent?? Lets say as of now i am using a Li ion battery, now I decide to place a Ni-cd battery , Will the chip predict the capacity still, Without much margin of error??

     

     

  • 0 in reply to Rakesh Muralidharan
    TI__Genius 14985 points

    For the IT gauges, it will NOT be erroneous if you insert a partially charged battery.  It must be properly configured and this process is not trivial, but once it is, it can use the voltage measurement to determine the initial SOC.  For more background and some videos, check this post:

    http://e2e.ti.com/support/power_management/battery_management/f/180/p/68227/247004.aspx#247004

     

    For the coulomb counting gauges, there is no way for it to detect the starting SOC of a partially charged battery that it is suddenly introduced to.  That's why they are usually used inside the battery pack.

     

  • 0 in reply to dMax
    Expert 2810 points

    As of now from I have cornered on BQ27510 as a suitable product and plan to place an order for the Evaluation Board.

    My only concern now is that I wont be having assigning a  fixed battery to my system though battery type may remain the same ,  there will be shuffling of batteries.

    For example I use battery A (3.7V, 3000mah) in system no. 1 today tomorrow after recharge i will be placing battery B (3.7V, 3000mAH)  to system no. 1. Even in this case

    can the chip offer me a better predictability than Normal voltage based measurements and coulomb counting method. i dont expect a very precise measurement but a better one compared to other two techniques??

     

     

     

  • 0 in reply to Rakesh Muralidharan
    TI__Genius 14985 points

    The system-side IT gauges, including bq27510, are designed to handle exactly the usage case that you mention.  As long as the batteries you swap out are the same models, the gauge will still give you very accurate results.  Even if one of the batteries is old (higher impedance and reduced capacity) and the other is new (lower impedance and original capacity), the gauge can learn the characteristics of them both and will store both profiles in memory.  When a battery is inserted and a load applied, the gauge will take a resistance measurement and compare it to the two known profiles stored in memory as well as to the default (original) profile.  It will then use whichever is the closest match to start with, and will further learn from that point on.

     

    See the section entitled BATTERY PROFILE STORAGE AND SELECTION starting on page 29 of the bq27510-G2 datasheet for more details.

    Just for future reference, if you need a gauge to support two completely different battery models, the bq27501 would be the best choice unless they both have the same capacity and similar OCV and impedance profiles.

  • 0 in reply to dMax
    Expert 2810 points

    what is the difference b/w BQ27510 and BQ27505-J4??  . leave the LDO part other than that how does BQ27505 determine the state of health (SOH) and BQ27510 does not??

    As of now I have plans to procure evaluation module for BQ27510 , what ever profiling i do for my battery model can it be used for other system side battery chips??

    Dont TI have an evaluation module for BQ27505-J4??

    lets say I insert a old battery (high impedance low capacity) to my system. If my system side gauge is BQ27510 then it will determine full 100% capacity or actual  drained capacity. Say I am inserting this old battery first time to the system.

    What will be the difference if i use BQ27505-J4 will in determine the capacity from the impedance data??