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BQ76952: Dcg/Chg Current Threshold

Andras Magyar
Intellectual 400 points
Part Number: BQ76952


Tool/software:

Dear Experts,

We use BQ76952 only to measure cell voltages and temperatures and

we still want to detect whether we are in charge or discharge state so

for example the over/under voltage and temperature faults and cell balancing

can be activated.

Since we do not measure the current we cannot decide it directly so my

idea was to set Dsg and Chg Current Threshold to zero so theoretically 

both of the protections (charge, discharge) are triggered if there is a fault.

My only doubt with this is that the description says that the current has to be above

the set Dsg and Chg Current Threshold and if my current is constant zero (plus some noise)

will it trigger any fault at all so 0 is ok? Look:

And also how will the cell balancing be decided if rest or charging state is present?

Can we give the BQ some info about this via some subcommand from another module

that measures our current?

Thanks,

Andras

  • 0
    Intellectual 400 points

    Hi,

    In the meantime I have just found and interesting comment in the manual of BQ which states that charging/discharging does not have to happen for for example

    OTC or OTD to be triggered, look:

    So it means that the protection triggers anyway regardless of the set current levels of charging discharging and relax states?

    Andras

  • 0 in reply to Andras Magyar
    TI__Expert 4320 points

    Hello,

    The OVP, UVP and temperature based protections should not be effected by being a charge are discharge state. However, for cell balancing, since the cell balancing while charging does depend on charge and discharge state I wouldn't set the Dsg Current Threshold to zero. 

    Since the current reading needs to be above the Dsg Current Threshold.

    Best regards,

    Thomas Rainey

  • 0 in reply to Thomas Rainey
    Intellectual 400 points

    Hi Thomas,

    Based on your answer, I have two further questions:

    (1) So if voltage and temperature protection triggers are not influenced by the rest, charge or discharge stated

    what bit is set in Safety Status B for a relexed state temperature fault when both discharge and charge is mentioned in this register? Will both be triggered?

    Please see below the highlighted ones I mean:

    For the voltage faults in Safety Status A there is no mention for charge/discharge though so I assume

    it is independent of the current as you had mentioned above:

    (2) This is regarding the cell balancing. So as I understand since we do not measure the current with this BQ and hence we do not have information about it the only way to have a stable cell balancing is for example is to set the discharge and charge current levels above the current noise measurement to make sure that we are in a stable relexed state? So for example Idchg= 200mA, Ichg=200mA. In this way we can only use relaxed cell balancing since the charging will not be detected, unless we use manual cell balancing. Am I right?

    Thanks,

    Andras

  • +1 in reply to Andras Magyar
    TI__Expert 4320 points

    Hello Andras,

    1. The description can be a little bit miss leading. UTD and UTC just determine whether you are turning off the discharge or charge FET. If both are set to the same value then both flags will trigger.

    2. Yes you are correct.

    Best regards,

    Thomas Rainey