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BQ25120A: Charge behavior if termination threshold is disabled?

Matthias Joerg
Prodigy 60 points
Part Number: BQ25120A

What is the behavior of the charger or how will the charging process be terminated if the TE bit (Termination/Pre-Charge and I2C Address Register) is set to disabled (= 0)?
Is there a rule of thumb for a general definition of the termination current threshold for standard LiPo batteries (3.7V nominal, 4.2V max.)?

What procedure do you recommend to charge a LiPo battery as gently as possible, e.g. only to 85-90% SOC? Is it possible for the bq25120a to terminate the charging process prematurely when the final charging voltage is reached (at the end of the CC phase, before entering the CV phase)? Or would it be better to set the end-of-charge voltage slightly lower (Battery Voltage Control Register set to < 4.2V, recommended values?)?

Thanks.

  • +1
    TI__Genius 12595 points

    Hello,

    If the charger's termination is disabled then the charger will continuously regulate the BAT pin of the charger to the regulation voltage. It will do this by pushing some amount of current towards the battery, the amount diminishes as it approaches the regulation voltage. This is typically recommended in order to avoid over-charging. For battery termination current it is best to check with the battery manufacturer to determine the optimal termination current, but this current will typically be on the order of C/10 current.

    If you are aiming to charge the LiPo to only 85-90% SOC then it is recommended to set the regulation voltage to a lower level. The only way to set termination current without some kind of ADC or gauging is to set a higher termination current, though the higher termination currents won't be found at the CC-CV transition point. It isn't recommended to skip the CV phase as this phase is meant to ensure that voltage at the cell is actually close to the regulation voltage, by accounting for the voltage difference from the BAT pin to the actual battery input.

    Ultimately, in my opinion, the best way to approach early termination is by reducing the regulation voltage of the charger and then allowing it to terminate in regular operation.

    Best Regards,

    Juan Ospina