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BQ24171: Where does the thermistor go?

Ed Landau
Prodigy 30 points
Part Number: BQ24171

We have a BQ24171 designed into out system to charge a Lithium Ion smart Battery.   The Smart Battery has an internal thermocouple which can be read using an I2C interface.  The engineer who designed out board though the BQ24171 were redundant so placed that thermocouple nowhere near the battery. As a result, the battery overheats and shuts down charging.  

Question: 

1) How does not attach the BQ24171 thermocouple to the battery in a reliable and consistent manner?  Must it be hot-glued to the body of the battery? Is having it "near" the battery sufficient?

2) Does TI make another battery which can be controlled thru an I2C interface and have its charge current reduced real-time programatically?  If so, my micro-controller could poll the battery's temperature and control the charge current manually.

Thanks

-Ed

  • 0
    TI__Mastermind 40315 points

    Dear Ed,

    1. The thermistor needs to be placed on the battery so that the temperature can be accurately sensed.

    2. TI does not make batteries. There are several chargers that have I2C interface and can control the charge current manually. I would suggest looking at the Battery Charger ICs below to find a charger that suits your needs.

    www.ti.com/.../overview.html

    Thanks,

    Mike Emanuel

    Please click "This resolved my issue" button if this post answers your question.

  • 0 in reply to Michael Emanuel35
    Prodigy 30 points

    Thank you for your reply.

    1) How does one affix a thermistor to a battery?  Hot-glue?

    2) Are there other charger TI makes that can be "pulsed" to turn on and off via an E2C interface so that my microcontroller can poll the smart battery's thermistor and control charging as a second-order control?

    Thanks,

    -Ed

  • 0 in reply to Ed Landau
    TI__Mastermind 40315 points

    Dear Ed,

    1) I would not recommend hot glue as the temperature of the gun applied to the cell could be damaging. I would recommend some sort of thermal expoxy, making sure the battery is not overheated upon application.

    2) Are you asking if the charger can act as a pass through sometimes and as a converter others? Please clarify what you are trying to achieve.

    Thanks,

    Mike Emanuel

    Please click "This resolved my issue" button if this post answers your question.

  • 0 in reply to Michael Emanuel35
    Prodigy 30 points

    Thanks for the hot-glue advice.

    The battery we are using is a smart-battery with an I2C interface and on-board thermistor which can be read thru that I2C interface. My micro-controller is awake during charging and can poll that battery's temperature and turn off the charger if it is getting too hot.

    Our current situation is the battery overheats and shuts down charging completely for a few hours until it has cooled.  I would like to be able to "pulse" the charger (or programmatically thru an I2C or SPI interface) control charging myself.   I have little confidence that we'll get the charger's thermistor is the right position on the battery reliably during manufacturing and with the right adhesive with the right thermal characteristics etc.  I want to make use of the thermistor that is already on the battery.  Does that make sense?  Am I being naive about this?

    Thanks

    -Ed

  • 0 in reply to Ed Landau
    TI__Mastermind 40315 points

    Ed,

    If you would like to use an external thermistor, I would suggest taking a look at Section 9.3.18 of the datasheet. You can program a resistor divider to indicate what temperature you use to cutoff charging to the battery based on temperature conditions using a thermistor. Figure 17 explains this very well. Just to clarify, the temperatures there are not fixed, they are dependent on your thermistor and resistor divider.

    You could program the temperature window for charging around the window of the smart-battery. If all goes as planned, you should have uninterrupted charging because you never reach the limits of the smart battery.

    As for the included thermistor, is there a way to connect it to the charging circuit? If not, you should use a microcontroller to pull the ISET pin voltage low (as shown in Section 9.3.2) in order to disable charging based upon your need.

    Thanks,

    Mike Emanuel

    Please click "This resolved my issue" button if this post answers your question.