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BQ77915: LD connection on Upper device of stack

Shivani Ghorpade
Prodigy 190 points
Part Number: BQ77915

Hello,

As per the fig 27 of datasheet, it is specified to use a diode on the upper device of stack for LD connection when we are using for UV fault recovery.

What is the recommended specification for this diode.

Regards,

Shivani Ghorpade

  • 0
    TI__Guru 54715 points

    Hi Shivani,

    It is a signal diode, almost any low current device should be ok.  Selecting a voltage can be more interesting.  For voltage LD can be as much as 30V below VSS.  If you consider a 10S battery with all cells depleted (0V) and a 42V charger attached, the limit for both parts would be exceeded. If all cells were at 2V and charge was off in the 42V charger, the bottom part would have LD at -22V, so it would not need the diode.  The top part would have LD at -32V, so it would need some diode protection since the pin alone can't support the voltage. Designers use different analysis methods and deratings, but often will select a diode with a voltage rating at or above the voltage of the pack.