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Trying to select a battery fuel gauge

Bob Pellegrino1
Prodigy 40 points
Other Parts Discussed in Thread: BQ35100, BQ34210-Q1

I’m working a new design to be used for upcoming programs. Part of the design requires an LED indicator that will light when a battery only has a certain amount of remaining charge (e.g. 25% remaining). The battery type is lithium thionyl chloride. This type of battery maintains its nominal voltage until it is very near end of life and then declines quickly to zero volts. So I think I can’t use a voltage comparator to determine remaining battery life. I think I need a fuel gauge. My other issue is that we want to monitor battery life when the unit is in storage. So we won’t have primary power available and won’t be able to communicate with the fuel gauge. In short I would need a fuel gauge that when running on battery power can:
1. Monitor battery charge
2. Provide an indication through an output pin when the battery is less than 25% of its total charge
3. Reset itself to initial conditions when the battery is replaced with a new one
4. Not need to use the I2C interface for the above requirements

One potential candidate is the TI bq34210-g. But I’m not sure if it can satisfy my requirements especially when I won’t have I2C communication capability. Any suggestions or potential designs would be greatly appreciated. It doesn’t have to be a fuel gauge if there is another way.

  • 0
    TI__Guru** 105770 points

    Hello Bob,

    I would recommend looking at the BQ35100, but our marketing team may refer you to a better gauge.

    The BQ35100 can do your first 2 functions and is designed for LTC batteries, but it needs to have a new battery command sent via I2C.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 40 points

    Thanks Wyatt. I looked at the BQ35100 but the new battery command sent via I2C is a show stopper for me. All I really need is something that will measure battery discharge and has a presetable discharge level in non-volatile memory that will trigger an alert when the discharge falls below the level. And when the battery is replaced it returns to its initial conditions of zero discharge and the presetable value. Are you familar with the bq34210-Q1? It seems that it might meet my criteria.

    Bob

  • 0 in reply to Bob Pellegrino1
    TI__Guru** 105770 points

    Hello Bob,

    The bq34210-q1 looks like it will perform the tasks you need. It may have trouble gauging your battery type well, LTC batteries are challenging to gauge. I would recommend getting the EVM and testing the configuration to see how well it will work. 

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 40 points

    Hello Wyatt,

    Thanks! I will definitely get the EVM and give it a try. If you know of any other options, especially one that  uses lower power please let me know. I notice that the bg34210-q1 uses 50 uA. Are you aware of any other TI alternatives that would meet my unusual criteria with lower power consumption?

    Thank you for your excellent support,

    Bob

  • 0 in reply to Bob Pellegrino1
    TI__Guru** 105770 points

    Hello Bob,

    Sounds great, I hope it works well for your application. There's no other gauges that I know of that has lower power consumption and your specifications. If something comes up soon I will put in another reply.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Prodigy 40 points

    Sounds good. Thank you Wyatt!