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BQ24171 battery charger IC not following CC/CV Process for lithium Ion

Akashay Singla
Prodigy 110 points
Other Parts Discussed in Thread: BQ24171

Hi Ti Team,

We are using BQ24171 IC in our portable device application. It charges the battery with 4.2V max. charging volatge with 1.4A max. charging current. We observed that it does not follow constant charging current condition upto 4.2V. Actually charging current drop from 1.3A to 1.0A  when battery voltage reaches upto 3.98V. So please provide us the best solution regarding this issue.

regards

Akashay Singla 

  • TI__Expert 5565 points
    Where are you measuring the battery voltage of 3.98V? At the SRN pin or the battery pack terminals? Remember that there is a wire impedance between the SRN pin and the battery pack terminals. This will cause the battery charger to see an elevated voltage at the SRN pin (charge current * wire impedance = elevated voltage). Therefore, if you are measuring 3.98V at the battery terminals when the current is <1.4A, it's probably because the charger is already seeing 4.2V at the SRN pin, causing it to think that it has already entered CV phase.
  • in reply to Smriti B
    Prodigy 110 points

    Hi Ti Team,

    We are using the same battery charger IC(BQ24171) to charge 2-Series batteries (Nominal Voltage 7.4V) with some modified circuit.

    Actual Battery voltage before charging is 7.51V. When i put battery for charging, at battery terminal it show 8.25V and at SRN terminal it shows 8.49V. So it does not follow "Constant Current" mode.Charging current continously decrease in mA. I understand the Elevated Voltage concept. But the difference between 7.51V and 8.25V is too high because of this it already enter into CV mode  before actual battery voltage is reached. So Please suggest us the best solution to control CC and CV mode.

  • in reply to Akashay Singla
    TI__Expert 5565 points
    Akashay,

    Please share your schematic so that we may review it.