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BQ29400 battery connection

Francois Cottin
Prodigy 30 points
Other Parts Discussed in Thread: BQ2085, BQ29400, BQ29330, BQ29412, BQ29311, BQ3060

Is it possible to use a connector to plug simulteanously the 5 wires of a 4-cell batteries on a circuit with BQ29400 and BQ2085?

BQ29400 documentation says "To prevent incorrect output activation the following connection sequences must be used. 4-Series Cell Configuration

· VC1(=VDD) ® VC2 ® VC3 ® VC4 ® GND or
· GND ® VC4 ® VC3 ® VC2 ® VC1(=VDD)"

But is this really mandatory or can we plug all-at-once? (much easier to implement in production and maintenance...)

Thanks for answer

Francois

  • 0
    TI__Genius 10235 points

    I know in the newer AFEs (bq29330) you can use a connecter to plug in the cells simultaneously. The biggest concern with the older parts is that the state of the cell balancing FETs is unknown at start up. So, if one FET is off and the rest are on, that one FET is taking the entire battery voltage drop accross it. Since it is only rated at 8V, it typically cause damage to the AFE.

    If you can get by with plugging them in sequence, I would recommend that. There is still a risk with simultaneous connection.

  • 0 in reply to Chase7071949597
    Prodigy 30 points

    Thanks Chase

     

    But if we use bq29330 instead of the bq29310, we will have to use the bq29412 instead of bq29400 and our problem will still the same, regarding bq29412 documentation: 

    "To prevent incorrect output activation, the following connection sequences must be used.

    4-Series Cell Configuration

    • VC1(=VDD) → VC2 → VC3 → VC4 → GND or

    • GND → VC4 → VC3 → VC2 → VC1(=VDD)"

     

    Am I right when I say we cannot use a connector even with bq29330 because of this bq29412 must-have?

    Francois

  • 0 in reply to Francois Cottin
    TI__Genius 10235 points

    The bq085 was designed to work with the bq29311 and the bq29400. Because both the AFE and protector have issues with incorrect cell connection sequence, you should follow the sequencing instructions in the datasheet. With incorrect sequence the bq29311 could be damaged and the bq29400 output could be activated inadvertantly, blowing your fuse. Since the detection time of the bq29400 is on the order of 1 to 2 seconds, you could use a connector that connects all cells at the same time. However, there is still risk of damaging the bq29311.

  • 0 in reply to Chase7071949597
    Prodigy 30 points

    The best way out our problem could then be to design with a newer generation, am I right?

    Which is the newer fuel gauge to replace bq2085 that would work along with bq29330 and bq29412 and then allow us the use of a connector?

    Is it complex to change from the older 3-set to the newer or is it about the same circuit logic?

  • 0 in reply to Francois Cottin
    TI__Genius 10235 points

    Yes. If you can do a new design, I would recommend upgrading to the bq3060. It uses the same gauging algorithm as the bq2085 (CEDV). It is also a single chip solution, rather than two chip. This means no AFE, since it is integrated into the same package as the gauge. So, you could use the bq3060 and bq29412 and have the same solution functionally as the bq2085, bq29311, and bq29400. It is also a much newer device, which means support for it will be better as well.