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BQ27510: BAT_LOW/BAT_GD Pin configuration

Thomas Faure
Prodigy 70 points
Other Parts Discussed in Thread: BQ27510, TPS65010

Hi,

I have an question about the BAT_LOW/BAT_GD Pin for BQ27510. 

If I understand correctly the datasheet, this pin is multiplexed between the battery state (full or empty) and the temperature. We want to use this pin only for monitoring the temperature.
0 = temperature is out of range. 1 = temperature is ok to charge.

For the moment in my configuration, the pin is set to low in the temperature is out of range, but also if the battery is empty... and if not good for me.

Thanks for you help!

Regards
Thomas

  • 0
    TI__Intellectual 2100 points

    The BAT_GD/BAT_LOW pin is a programmable GPIO with varying behavior. 

    It can be BAT_LOW: which indicates (as you mention) when the battery is at low state of charge.  In this case, the pin tracks the bit SOC1 in the flags register.  Note that it is programmable active high or active low.

    It can also be BAT_GD: which indicates a number of things depending on the PFC (pin function code) prgrammed into the operation configuration register.  It is also programmable active high or active low.  The PFC's are documented in the datasheet, but I'll summarize below:

    The four PFC's are:

    00: Gauge and Charger independent: BAT_GD always high impedance, gauge uses thermistor during discharge and relaxation

    01: Temperature monitored during charging: if temperature falls outside of programmed temperature range, BAT_GD becomes false, which would typically disable the charger.

    10: Gauge shares thermistor with charger.  BAT_GD is high-impedance

    11: Temperature monitored during charging: gauge uses BAT_GD to disable charger if temperature conditions fail just as in PFC=01.  The only additional functionality is that the guage ALSO disables the charger via BAT_GD when the FC (full charge) bit is set.

     

    From your application, it seems you would want to configure your gauge to use BAT_GD with PFC=01 or PFC=11 with active high.

    Let me know if this helps,

    Charles

  • 0 in reply to Charles Herder
    Prodigy 70 points

    Hi Charles,

    Thanks a lot for your quick answer, I understand everything... and it works!! (I but the BAT_FN = 1 (so BAT_GD) and PFC = 01)

    Just an remark, inside the datasheet, the configuration PFC=11 (0x03) is not explain, why?

    Thomas

     

  • 0 in reply to Thomas Faure
    TI__Intellectual 2100 points

    Good catch! 

    This was a firmware change.  Very few people use PFC=0x3 so we removed it in newer firmware revisions.

    Charles

  • 0 in reply to Charles Herder
    Prodigy 70 points

    Sorry, but there are other questions about the BAT_LOW/BAT_GD functionality pin,

    Do you think is possible the to put the BAT_LOW/BAT_GD to low when the temperature is outside the range and to put BAT_LOW_BAT_GD pin to higt impedance when the temperature is inside the range. In fact, it is necessary to change the BAT_LOW/BAT_GD pin polarity....

    For this:
    I put the BAT_FN = 1 (because I don't want to use the pint BAT_LOW/BAT_GD for the battery status)
    I put the PFC = 01 (temperature is monitoring during charge like you explain me!)

    and how to configure the BATL_POL and BATG_POL ?
    BATL_POL is normaly use for invert the state of pin when BAT_FN = 0, is correct? It can be also inverte the status of pin when BAT_FN = 1?
    I don't really understand the functionality of BATG_POL.

    The main idea is connect directly the BAT_LOW/BAT_GD pin form BQ27510 to TS pin to TPS65010...

     

     

  • 0 in reply to Thomas Faure
    TI__Intellectual 2100 points

    Thomas,

    The BAT_GD/BAT_LOW pins are open drain connections. In this configuration, the port can either be high impedance or low impedance to ground.  The BATG_POL and BATL_POL pin configures which of these states corresponds to a "true/false" value.

    For your purposes, you will be configuring the BATG_POL.  Since you are not using BAT_LOW, you can ignore its polarity bit. 

    You have correctly stated that BAT_FN=1(use BAT_GD instead of BAT_LOW), and PFC=01.

    Now, if you want BAT_GD to be high impedance when the temperature is inside the range and low when the temperature is outside the range.  This means that BAT_GD will be active high.  Therefore, BATG_POL needs to be '1' .

    Let me know if this helps,

    Charles

  • 0 in reply to Charles Herder
    Prodigy 70 points

    Charles,

    Thank you for theses informations. I put BATG_POL = 1 to invert the polarity pin, and BATL_POL = [don't care] in my case!

    Other point, just for confirmation:

    When the battery is connected to the fuel gauge, The track algorithm should measure the battery voltage in open circuit (Ibat < C/20) it's correct?
    During this stage, can you confirm that BAT    _LOW/BAT_GD pin is set to low (ground) in my case (BAT_FN = 1, PFC=01, BATG_POL=1, BATL_POL = [don't care]) ?

    Do you also know the current can be drived by the BAT_LOW/BAT_GD pin. I do not find the value inside the BQ27510 datasheet.  The current come from the TS pin (in TPS65010) is below 100µA. So I think the mosfet inside the BQ27510 can drive this current correct?

    Thanks for support!

    Thomas

  • 0 in reply to Thomas Faure
    TI__Intellectual 2100 points

    Thomas,

    If BATG_POL is '1', then the BAT_GD pin will be high impedance when the battery is "good".  In a pull-up configuration, that means that the pin will be high when the battery is "good".

    I am confirming the following:

    When the battery is connected, the gauge will initially measure the OCV of the battery.  Until the gauge gets a good OCV measurement, BAT_GD will be FALSE.  In your case, this will correspond to the gauge pulling the BAT_GD pin to ground.  When the gauge gets a good OCV measurement and confirms that the temperature is good, then the gauge will set BAT_GD to TRUE.  In your case, this will mean that the gauge will eventually bring BAT_GD into a high-impedance state.

    Details on the open-drain specification:

    There isn't a specific rated current for the BAT_GD pin, but we do know the following: It is an open drain connection, so it can only sink current.  From the spec, the V_OL is rated to 0.4V at 3mA, which corresponds to an maximum ON resistance of about 133 ohms to ground.  In reality, I have measured this to be significantly less (usually on the order of 30-50 ohms).  

    Is this enough information about the pin specification, or do you need some idea about how much power we can dissipate into the die?

    Thanks,
    Charles