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BQ77915: Recommended Output Panel FET

CHO SR
Genius 3415 points
Part Number: BQ77915

Hi,

Customers use BQ77915 for two BMS projects.

* BMS Setup Specifications

- Chemistry(Capacity) : Li-ion(1.9Kw), LiFePO4(2.5Kw)

- Cell balancing type : External FET

* Configuring Batter Pack

- 18650 2500Ah Li-ion : 4S45P

18650H8-2500mAh .pdf

- LiFePO4 206A : 4S

EP-12.88V206Ah.pdf

The quantity of the output terminal FET has increased due to the large battery capacity.

To increase the turn off speed, refer to Datasheet and add the following circuit.

Please recommend the available 'Q9' FET product.

  • 0
    TI__Guru 54715 points

    Hi CHO,

    See section 3 of the application note https://www.ti.com/lit/pdf/slua773 for discussion of Q9 recommendations.  Q9 does not need to be high voltage or high current, it will pull down the gates with some mA.  It is recommended to have low Vgsth so that it is on after the power FETs are off. Low Vgsth often means the maximum Vgs is low, so D3 is a zener in the diagram. If  you have a FET with Vgs maximum of 20V D3 be a standard diode.  A general purpose P-ch FET like a BSS84 might be appropriate. Some circuits will use a PNP for this function but since it has current gain, a smaller R17 is likely needed resulting in more standby current.