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BQ76952: Clarification on some register settings

Steven Hunter
Intellectual 420 points
Part Number: BQ76952
Other Parts Discussed in Thread: BQ76942

1) Why is the default "Power:Shutdown:Shutdown Stack Voltage"   600*10mV? This seems very low for any reasonable stack of cells.

2) What is a good value for "Power:Sleep:Sleep Charger Voltage Threshold"? Why block SLEEP mode?

3) The default for "Settings:Cell Balancing Config:Cell Balance Min Cell V" seems very high (3.9V). Why not balance at lower voltages?
4) Is "Power:Shutdown:Shutdown Stack Voltage" a lower limit? A 6V default seems very low for any reasonable stack of cells.

5) Why block SLEEP mode when "Power:Sleep:Sleep Charger Voltage Threshold" is below 20V?

Our configuration is:

9 cells: Cells 1-8 &16. (yes I know that we could have used the BQ76942)

Standalone operation (no processor)

No Fuse

One temperature sensor

Max 4amp charge, 8amp discharge

This system is for an experiment, not production.

Deepcore Battery Settings.gg.csv

  • 0
    TI__Mastermind 25850 points

    Hi Steven,

    Steven Hunter said:
    Why is the default "Power:Shutdown:Shutdown Stack Voltage"   600*10mV? This seems very low for any reasonable stack of cells.

    The device supports as few as 3 cells, so the default has to be low to allow any customers with a 3s application to start the device successfully.

    Steven Hunter said:
    What is a good value for "Power:Sleep:Sleep Charger Voltage Threshold"? Why block SLEEP mode?

    This value is dependent on your application. This setting is available if the customer wants the device to not enter SLEEP mode until the battery is fully or near fully charged.

    Steven Hunter said:
    The default for "Settings:Cell Balancing Config:Cell Balance Min Cell V" seems very high (3.9V). Why not balance at lower voltages?

    You may change the setting to allow balancing at lower voltages.

    Steven Hunter said:
    Is "Power:Shutdown:Shutdown Stack Voltage" a lower limit? A 6V default seems very low for any reasonable stack of cells.

    This setting will trigger the device to enter SHUTDOWN mode when the total stack voltage is below this threshold. As I mentioned before, in a 3s application, 2V/cell is a reasonable point to trigger shutdown. For higher cell counts, the customer may have to change this setting.

    Steven Hunter said:
    Why block SLEEP mode when "Power:Sleep:Sleep Charger Voltage Threshold" is below 20V?

    The main reasoning is likely to keep both FETs on and to have the measurement loop running at full speed during charging.

    I gave your settings a quick look and they seem fine. One thing I want to note is that your TS1 Config has the pin set for a general-purpose ADC input. You may consider setting it to 0x07 if you intend to use it for temperature protections, or 0x0B if you just want to report the measured temperature but not use any protections.

    Regards,

    Max Verboncoeur

  • 0 in reply to Max Verboncoeur
    Intellectual 420 points

    Thank you very much for your insight and quick reply.