Purpose of pass resistor and MOSFET on LT8584's datasheet's Typical Application section

Hi ogzhn177 ,

It seems to be a passive balancing circuit, for a configuration where there are more than one module in series. You can omit the FET and pass resistor if the module plugs directly to the charger.

See LT8584 datasheet, page 33, right column, point 5.

Cheers, heke

Thank you for pointing out.

But why would we need passive module balancing if we have active balancing solution. Do you think it's a safety measure if active balance circuit fails or something?

Hi ogzhn177 ,

The active balancing works with-in a module. Another balancing is seemingly needed if several modules are connected in series. In principle it might work that the fly-back outputs are connected to the terminals of the whole stack of modules and with IsoSPI bus the balancers can float. I do not know why passive balancing is preferred here instead. Could indeed be a safety reason or serviceability issue.

Cheers, heke

Hi Heke ,

Thank you for your answer. OK I think I get it know. If a complete module is out of balance than you need to balance that module compared to other module voltages. Then I guess re routing the excess charge to whole battery pack would be more ideal. But again that would complicate the harness so there is a trade of between two solutions. 

You've been very helpful. Thanks again. 

Thanksogzhn177 ,

I think you wrapped it up nicely. In case of further doubt, ADI's FAE people may be a good contact point.

Cheers, heke

Thanksogzhn177 ,

I think you wrapped it up nicely. In case of further doubt, ADI's FAE people may be a good contact point.

Cheers, heke