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BQ4050: BAT-Pin Connection diode and resistor

Klaus
Expert 1431 points
Part Number: BQ4050
Other Parts Discussed in Thread: BQ40Z80, BQ40Z50

Hi Ti Experts,

we want to develop a BMS for a 1S2P (6700mAh) battery with the bq4050.

In the datasheet I have seen that the BAT Pin is connected to battery plus over a shottky-diode.

As I know from the bq40z80 there we use an additional 100Ohm resistor.
I think it protects the diode when the BMS is connected to the battery the first time.
We have used it because it is written in the datasheet from the bq40z80.

Should we also us a 100Ohm resistor in our design of the bq4050?

Thanks for helping us.

Klaus

  • 0
    TI__Guru** 105600 points

    Hello Klaus,

    I believe since the BQ4050 has a lower stack voltage than the bq40z80 the designers thought the 100ohm resistor was needed for the bq40z80 to help reduce some of the transients.

    I will need to check with someone on the team to confirm, but if it is on the EVM it is to the designers specs.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Expert 1431 points

    Hi Wyatt,

    thanks for your answer.

    Please let me know if someone from the team has confirmed it. I will act accordingly.

    Thanks.

    Klaus

  • 0 in reply to Klaus
    TI__Guru** 105600 points

    Hello Klaus,

    I have checked with someone else on the team, it is most likely because the higher stack voltages and to prevent large current draw in case of an internal short in the gauge.

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Expert 1431 points

    Hi Wyatt,

    thanks for your answer.

    Is ist possible that the bq40z50 can get an internal short circuit?

    If yes we should also use the resistor in a bq40z50 application, isn't it?

    Thanks for your help.

    Klaus

  • 0 in reply to Klaus
    TI__Guru** 105600 points

    Hello Klaus,

    It is always a possibility with any IC for an internal short, if you are concerned with it I would test putting a series resistor on an EVM, it should not affect the gauge much since it uses very little current. I have never heard of our gauges experiencing an internal short before so it would be precautionary .

    Sincerely,

    Wyatt Keller

  • 0 in reply to Wyatt Keller
    Expert 1431 points

    Hi Wyatt,

    thanks for your answer.

    Ok. I think I will not plan to use it in the new design.

    As you mentioned I will test it on the EVM maybe.

    Thanks for your help.

    Klaus