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bq77pl900, host control mode - does it continue to monitor cell V for under-voltage automatically? Or only when I measure a cell V myself?

bq77pl900, host control mode - does it continue to monitor cell V for under-voltage automatically? Or only when I measure a cell V myself?

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Brian Myers
Posted by
on Jul 09 2009 23:08 PM
Prodigy190 points

I suspect that it continues to monitor the cells at a 50 millisecond sample rate, just as in standalone mode (Otherwise, what's the point of the FS bit in OUTPUT_CONTROL?)

A fellow engineer believes that in host-control-mode, it only measure cell V's when the host measures cell voltage at V_OUT, but I believe measurement of cell V externally is not required for UV protection to occur. If he's right, I really need to switch to standalone mode whenever my processor goes to sleep. If I'm right, host-mode is all I need.

bq77PL900 battery
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  • WM5295
    Posted by
    on Jul 13 2009 13:46 PM
    Expert3270 points

    Yes, sampling of the cells for safety continues in host mode at the same rate as standalone mode.

    Measurement of the cell voltage by the host through the cell monitor features is not required for the device to continue to operate with its pre-programmed safety limits in host mode, even if the host is disconnected or asleep.  Some other thoughts when putting the host to sleep:

    • When the host wakes up, it will need to take action to recover from any safety events which occured while it was asleep.
    • If more restrictive protection limits are implemented in host code, these will not be available while the host is asleep.
    • XLAERT might be used as a signal to wakeup a host on a safety event, circuitry is implementation dependent.
    • Cell monitoring output circuitry does increase the supply current, these outputs might be turned off before putting the host to sleep.
    • Cell balancing is controlled only by the host in host mode; it will remain active while the host is asleep, so turning off balancing before putting the host to sleep may be desired

     

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