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BQ24192: Battery drop issue while discharging

Sahil Nayak
Intellectual 450 points
Part Number: BQ24192

Hi TI Team,

We are using BQ24192 charger chip in our custom design. 

When our system is drawing 2.5A constant current and if we remove the external input, the system draws 2.5A current from fully charged battery.

At that time, We are seeing 250mV difference between the voltage at battery terminals and voltage at system output (VSYS) which in turn causes the reduction of available voltage to the entire system.

To clarify, voltage at battery terminals is 250mV greater than that at system output.

Please help us to debug this issue further.

Note: Battery was full charged when migrating from external input to Battery.

  • 0
    TI__Guru** 102355 points

    Hello Sahil,

    What is your trace resistance between the two nodes? This is more likely due to board layout because when the charger is just supplying power from BAT it just leaves the BATFET active, which has 12mOhm resistance which would be only a 30mV drop, the rest of the voltage drop must be from layout or long wires to the battery connection.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Intellectual 450 points

    Hi Wyatt,

    Thanks for your quick response.

    We have routed the two nodes with a thick plane. Please see attached snapshot for more clarification.

    Also, please see the attached snapshot of schematic.

  • 0 in reply to Sahil Nayak
    TI__Guru** 102355 points

    Hello Sahil,

    What nodes are you measuring? Are you measuring at the pins of BAT and SYS of the charger to get the voltage differential? If there are any traces or connectors in-between it that may lead to your voltage drop.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Intellectual 450 points

    Hi Wyatt,

    In reference to the schematic snapshot shared in my previous reply, we are measuring at TP38 with respect to GND and TP105 with respect to GND. 

    The difference between TP38 and TP105 is around 250mV.

  • 0 in reply to Sahil Nayak
    TI__Guru** 102355 points

    Hello Sahil,

    I'm not sure where the test points are on the layout, that is the more critical question. Please measure the differential at the pins of the charger. As I mentioned the BATFET resistance is very low, the voltage differential you're seeing is most likely from the layout/connectors/wire losses and not from the charger.

    Sincerely,

    Wyatt Keller