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BQ77905: Over-Current Detection

user4931135
Prodigy 40 points
Part Number: BQ77905

Hi,

I am planning to use BQ77905 in one of my project but I have a question. There is no spesific determination about over-current in discharge protection. It says that over-current detection voltage can be between 10 to 85 mV, but there is no information about how to set these voltage.

Thanks,

  • 0
    TI__Guru 54715 points
    Hi,
    The bq77905 is programmed at the factory. For overcurrent protection the 10 to 85 mV is the possible range of the part, table 3 in the data sheet shows a summary of the options possible. However a specific part number will have a single value for each setting. See table 2 for the configurations which are currently orderable. If you are interested in a configuration which is not currently available, contact your local TI representative.
  • 0 in reply to WM5295
    TI__Guru 54715 points
    Hi,
    If you have desired settings for a configuration you would find helpful for your future designs, you might post here. It may help define a future device version.
  • 0 in reply to WM5295
    Prodigy 40 points
    Hi,
    You recommend 1 mOhm for Rsns in the documents of bq77905. If I decide to use 2 or 5 mOhm, does it cause a problem? And why there is two different OCD in this IC. I can't fully understand from the documents.
  • 0 in reply to user4931135
    TI__Guru 54715 points
    Hi User,
    The bq77905 sense input responds to voltage levels. Changing the sense resistor is fine, you may notice the EVM used a 10 mOhm resistor. Since the bq77905 thresholds are programmed at the factory, to change the current trip points for a battery design, either select a different configuration (bq77905xx) or change the sense resistor. Of course be sure to plan for the power dissipation in the sense resistor whether it is 1 mOhm or another value.
    The bq77905 has 2 OCD thresholds, OCD2 has a higher threshold for a shorter time. You might think of OCD1 as limiting the maximum steady current while OCD2 limits the maximum surge current. SCD provides a still higher threshold at a very short fixed time for a short circuit or heavy overload condition.