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BQ76200 Part Selection

user2012342
Prodigy 70 points
Other Parts Discussed in Thread: BQ76200, BQ76925, LM5060Just discovered BQ76200, do you think it's suitable for my design? I'd use only one ENABLE signal, so both FETs would be either ON or OFF. (no separate CHG and DSG) Does BQ76925 + BQ76200 combination meet my requirement of fast turnoff while short circuit? Do I even need a series inductor? (I have 5S Li-Ion akupack and ~5mOhm FETs, the short circuit current might be like 100A?)

Many thanks
Tomas
  • 0
    TI__Genius 12621 points
    Hi Tomas,

    I split this thread so that the Battery Chargers team can help you with part selection.

    This thread was split in reference to here:
    e2e.ti.com/.../636814

    Thanks!
    Alex
  • 0 in reply to Alex Triano
    TI__Guru 54715 points

    Hi Tomas,

    A battery design typically allows the battery to provide full current to the load rather than limiting current.  Current is monitored and if too high it is switched off with various thresholds and times. The bq76925 and bq76200 are designed for battery applications.  With the bq76925 the switching is normally controlled by the system MCU with a rapid response from the current comparator.  You would need to analyze and test to determine if the response is fast enough or if a supplemental fast response circuit is needed for the short circuit condition.

    During short circuit the bq76200 keeps the FET gate on using the CVDDCP capacitor.  Examples are shown in the FET Configurations apnote slva729.   If the short is long enough that the charge pump cap voltage falls the IC will turn off from UVLO, but it would be preferred to have the control circuit turn off the driver with the enable. With a battery protection switch the FET switching is typically slowed to avoid exciting the cell inductance during switching at high current which can induce a high voltage transient which then must be filtered or clamped in the battery.  The bq76200 has the internal resistance which will limit the gate pull down current, and the switching architecture pulls the gate voltage to the PACK pin.  This is different than the LM5060 and the bq76200 will not achieve the pull down current of the LM5060 noted in the other thread. The CVDDCP capacitor can be scaled up for the larger FET capacitance, but turn off will slow since the internal resistances do not scale.  Be sure the FETs stay in their safe operating area. When designing with the bq76200 also see the apnote slua794 for component selection considerations.   The LM5060 provides an excellent driver, I'm not aware of a reference showing its use in a battery application.  If implementing this type design Alex may have better guidance,  some considerations would be load on the battery, avoiding excess currents in the LM5060 and keeping the gate voltage in a safe range.