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BQ24170: VSYS and VBAT maximum current

Rafael Moraes
Prodigy 60 points
Part Number: BQ24170
Other Parts Discussed in Thread: CSD17313Q2, CSD17318Q2

Hi TI,

The BQ24170 datasheet states that the charger has integrated 4-A MOSFETS and maximum battery charge current is 4 AMP.

My question is if this current limitation also affects the current through VSYS?

My system needs to charge the battery up to 2 AMPS only, but the VSYS load is 6AMPS.

I currently use this charger in a lower power application, so ideally I would use the same part for this higher power application.

If this part does not meet the requirements, what would the recommended stand-alone charger for a 3-cell Li-Ion battery to support up to 8A total current?

Thanks,

Rafael

  • 0
    TI__Guru**** 170196 points

    Hi Rafael,

    Since the input/adapter is passed through to VSYS by FETs, that current is limited only by the AC and RB FETs.  If the charger input current limit feature is used and the VSYS current exceeds the charge input current limit, no current goes to the charge the battery.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 60 points

    Hi Jeff,

    Thanks for the clarification.

    So I should be able to use the BQ24170 to charge a 3-cell battery at 2 AMPS and power a VSYS load of 6 AMPS as long as:

    1. The power supply has enough power. (Will use 15V, 225W PSU).

    2. Substitute both CSD17313Q2 FETs which are limited to 5A to higher current FETs.

    3. Configure IDPM to 15 AMP by adjusting VACSET to 6V.

    4. Configure ICHARGE to 2 AMP by adjusting VISET to 0.4V.

    Can you recommend any FET from TI to substitute both CSD17313Q2?

    best regards,

    Rafael

  • 0 in reply to Rafael Moraes
    Prodigy 60 points

    Considering the CSD17318Q2.

  • +1 in reply to Rafael Moraes
    TI__Guru**** 170196 points

    Hi Rafael,

    VACSET max is 3.6V.  IDPM does not limit the current through the AC and RB FETs.  It only reduces the amount of current that the converter uses to charge the battery.  For example, if your system needs 15A or more, with ICHG=2A and IDPM =15A, the charge current from the current is 0A because IDPM is active. The system gets its 15A+ with no issue.  

    CSD17318Q2 is a good choice.

    Regards,

    Jeff