• State Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 399 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ35100: Battery monitoring below 2.70V

Robert Brown66
Prodigy 100 points
Part Number: BQ35100
Other Parts Discussed in Thread: INA230, INA233

Hi Group,

I have to design a fuel gauge for an LiSOCL2 (thionyl chloride battery) but there's a snag. The system has an external supply. To prevent charging the battery there's a diode in series, and to allow headroom of voltage drop, my spec calls for a 2.70V supply voltage. The bq35100 has a lower voltage limit of 2.7V, and my review panel rejected the use of the chip on this basis.

<rant>

Many micros and analog chips work down to 1.8V, so it's strange that T.I. (or anyone else) can't make a battery monitor that works below 2.7V !

</rant>

I reckon the bq35100 is developed from the venerable INA230 I2C, which was repackaged several times with small changes as the INA233, etc. Hence the 2.7V supply floor.

So does anyone know of a battery monitoring chip like the bq35100 or even the INA230 which will work at 2.6V? I went through Mouser/Digikey etc, but can't turn up anything.

Regards,

Rob

  • 0
    TI__Guru* 76230 points

    Hi Robert,

    The bq35100 can work down to 2.45V. It is just that below 2.7V, there will be no flash writes  to the gauge. To circumvent this, you can use >1 s cell config or you can boost the voltage with extra components to higher than 2.7V

    thanks

    Onyx

  • 0 in reply to Onyx Ahiakwo
    Prodigy 100 points

    Hi Onyx,

    You are right that the bq35100 provides some functionality <2.70V, but the gauge enable (GE) high level enable voltage is 2.65V. See section 6.6 of the datasheet. My review panel also points out the power regulator has a 2% tolerance, so can be 2.65V, hence no margin on the enable.

    A boost power supply would work, but add cost and current to the design. I have neither option. The LTC3335 (dare I mention the other company...) does work down to 1.8V but costs $3.30.

    Unless I can find a battery monitor that works down to 2.5V, the solution will have to be using my micro to do battery monitoring. The firmware guys will hate me for giving extra work.

    Sometimes engineers just cant win!

  • 0 in reply to Robert Brown66
    Prodigy 100 points

    I moved onto a plan B,

    So closed this thread.