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BQ24075: How to find connection/Disconnection of Li-Battery on BAT1&2 Pins?

NANDHA KUMAR
Prodigy 90 points
Part Number: BQ24075

Hi Team,

We are using BQ24075RGTT on our existing product ( Kindly refer current schematic below )

 

We would like to use the same section on another new product. In the previous product, we had a challenge finding Li-battery connection & disconnection. Since we are getting 0-3.5 Waveform from BAT1&2 pins while Li-battery is not present. We are not able to detect the disconnection of the Li battery from the device. ( i.e, Always getting voltage at  AIN_LIBAT_MC uC input so not able to find the disconnection )

We hope there is a possibility to find the battery disconnection & connection in this charger IC. Kindly review the above schematic & assist us to achieve the above function ( Li-batt connection/Disconnection )

  • 0
    TI__Genius 12475 points

    Hi Nandha,

    You are correct- it can be challenging to determine the battery disconnection when adapter is present and charging is enabled. We are reviewing your circuit. 

    Meanwhile I have a question on your use case- how often do you intend to check for the battery presence? When the adapter is present- do you intend to disable charging and then check for the voltage? 

    Regards,

    Gautham

  • 0 in reply to Gautham
    Prodigy 90 points

    Hi Gautham,

    As per customer requirements, we need to identify the internal battery ( Li-batt ) disconnection/Connection event immediately. So we will check Li-Batt presence frequently by using our application logic. for that only we required valid logic that needs to be followed. We hope we can get constant 2volt on the BATT pin while the battery is removed by using some mode is that correct? If yes kindly assist us to achieve the same.

    Yeah, you are correct, If we want to measure Li-Batt voltage We will stop the charging process by using BATT_CE uC pin & then we will measure the voltage at AIN_LIBAT_MC ADC output on the BATT pin. 

  • 0 in reply to NANDHA KUMAR
    TI__Mastermind 23170 points

    Hi Nandha,

    With the 1k resistor R65 pulling the BAT pin to GND, this may not be enough to exit the waveform portion of the battery detect. You'll need to decrease the resistance to overcome the current that is used during the battery detection routine. To get the 2V you desire, you would need 250 Ohm resistor pulling BAT to GND.

    Be aware, this may lengthen the time on the battery safety timer if using this method. 

    Are you able to control the CE pin? Pulling this pin high while battery is disconnected will not show the battery detect routine and the voltage will fall to about 750 mV from my testing.

    Best Regards,

    Anthony Pham

  • 0 in reply to Anthony P Pham
    Prodigy 90 points

    Hi Anthony

    Noted, We need to change the value of R65 to 250Ohms to get 2V constant output from BAT pin if batter disconnected. Is my understanding correct?

    lengthening the time on the battery safety timer is due to 250 Ohm resistor replacement on R65 position? will this affect any function of the system?

    Yeah, able to pull up & pull down CE Pin with help of uC by using the above circuit (i.e, Able to Enable/Disable charging mode with above design).

    1. While having the battery is disconnected & charging is enabled condition BAT pin won't give 2V constant output ( Battery detection routine ) is that correct?

    2. We are getting 0-3.5V sine wave while having the battery disconnected & charging enabled condition. Is this expected? How to identify battery disconnected events while having the above condition? 

  • 0 in reply to NANDHA KUMAR
    TI__Genius 12475 points

    Hi Nandha,

    The waveform should look similar to below. I don't expect a sine wave- can you share the waveform?

    What Anthony was referring to was to have a pulldown that can fail the battery detect routine. 

    Regards,

    Gautham