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Question about Voltage gap between lowest battery and other batteries in system used LTC6803-4


My customer use LTC6803-4 and I attached around circuit diagram of LTC6803-4.

They say that their system is consisted of connecting 1 ~5 ea LTC6803-4s.

During use this circuit, they got some issue like below. 

    1) Issues

      If they use their system connecting over 2 LTC6803-4s, they say that vantage value of  lowest battery is lower 0.1V ~0.2V than other batteries.

      And this voltage Gap is increasing as time passes.


     2) Questions

       2-1)  Would your check attached their schematic (Schematic-1.pdf, Schematic-2.pdf)  and let me know your opinions?


      2-2) Would you advise how to handle V+ pin?

             They guess that the root cause of above issue is a handing method of V+ pin.


       2-3) Would you advise how to handle TOS pins ?

           In your datasheet, it seems that  TOS pin of LTC6803-4 connecting highest battery should be connected to VCC, and other TOS pins should be connected to GND.

          2-3-1)  Is above thing right?

           In  attached schematic,  TOS pins are NC. 

           So they want to know the effect if TOS pin is NC.

           2-3-2) Would you suggest your opinions about the effect if TOS pin is NC?

Please help them.









  • Error on cell1 of the IC will usually come from resistance between the cell and the circuit, though 0.2V is a lot of error. The floating TOS could be a contributor (see below).

    For Q2-1: The circuit looks normal to me, but L15 might best be shorted so that there wouldn't be so much opportunity to forward-bias D17 when supply current flows.

    For Q2-2: The V+ pin looks properly connected.

    For Q2-3: The TOS logic state is probably a 'don't care' for this application, but it is not good to float a digital input since some [non-logic] voltage levels can induce a lot of supply current. TOS should be connected to either Vreg or V-.