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BQ25886: About a protection FETs for a battery

Yuta Nishie
Genius 4295 points
Part Number: BQ25886
Other Parts Discussed in Thread: BQ25792, , BQ34Z100, BQ76905, BQ77307

Tool/software:

Hi,

I would like to manage the battery in a BQ25792 or BQ25886 + BQ34Z100 configuration.

I have a question about how to control the Protection FETs described in the Simplified Schematic of the BQ34Z100.

1. Can I control the Protection FETs using the SDRV pin of the BQ25792?

2. Is it correct that the BQ25886 does not have a pin to control the Protection FETs, so I need another IC?

Best Regards,

Nishie

  • 0
    TI__Guru 55321 points

    Hi Nishie,

    For Q2, the BQ25886 does not have the pin.

    We will get back to you on Q1.

    Thanks,

    Ning.

  • 0 in reply to Ning T
    Genius 4295 points

    Hi Ning-san,

    Thank you for your support.

    Could you tell me the recommended protection FET control IC that can be used in combination with the BQ25886?

    Best Regards,

    Nishie

  • 0 in reply to Yuta Nishie
    TI__Guru**** 160721 points

    Hi Nishie,

    792 SDRV cannot be used to control the protection FET.

    Regards,

    Jeff

  • +1 in reply to Yuta Nishie
    TI__Mastermind 41770 points

    Hello Nishie-san,

    Is this a 2s system? If so, the device that could fit here for protections with FETs would be the BQ76905, this is a 2s to 5s battery monitor and protector with low-side FET drive to use with its integrated protections.

    It can do current/voltage and temperature protections to protect the battery and provides the ability to cell balance your cells by using your MCU.

    You need to use your MCU to interface with this monitor device. An alternative is the BQ77307 protector, which also would require an MCU and it is very similar to the BQ76905, without any monitoring capabilities and without cell balancing capabilities.

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Jeff F
    Genius 4295 points

    Hi Jeff-san,

    Thank you for your support.

    I understand that 792 SDRV cannot be used for protection FET.

    Best Regards,

    Nishie

  • 0 in reply to Luis H. S.
    Genius 4295 points

    Hi Luis-san,

    1. Thank you for introducing BQ76905 and BQ77307. These ICs have VC0 to VCx pins, do I need to connect these pins to the battery? My battery is 2Cell, but I cannot connect it to VCx because there is no terminal between 1Cell and 2Cell.

    2. Also, the Protection FETs of the Simplified Schematic of BQ34Z100 are connected to PACK+, while the FETs of BQ76905 are connected to the PACK- line. Am I correct in understanding that the protection purpose is different?

    Best Regards,

    Nishie

  • +1 in reply to Yuta Nishie
    TI__Mastermind 41770 points

    Hello Nishie-san,

    Yes, these are meant to connect to the battery. If that is not possible, you may need to have another circuit to perform the protection. 

    The charger itself may have some protections related to the battery, but it would not control MOSFETs.

    Yuta Nishie said:
    2. Also, the Protection FETs of the Simplified Schematic of BQ34Z100 are connected to PACK+, while the FETs of BQ76905 are connected to the PACK- line. Am I correct in understanding that the protection purpose is different?

    No, they achieve the same function, of protecting the battery. This is a low-side FET driver instead of high-side FET driver. Each may have some differences.

    Best Regards,

    Luis Hernandez Salomon

  • 0 in reply to Luis H. S.
    Genius 4295 points

    Hi Luis-san,

    Luis H. S. said:

    Yes, these are meant to connect to the battery. If that is not possible, you may need to have another circuit to perform the protection. 

    The charger itself may have some protections related to the battery, but it would not control MOSFETs.

    If you have a reference design for another circuit for protection, please share it.

    Best Regards,

    Nishie

  • +1 in reply to Yuta Nishie
    TI__Mastermind 41770 points

    Hello Nishie-san,

    We do not unfortunately. The monitor/protector devices are meant to be inside the battery pack to protect each individual cell. You could use high-side FET drivers or ideal diodes with an MCU to provide simple protections. 

    Best Regards,

    Luis Hernandez Salomon