Application Question for LTC6810 and similar parts.  It's not required to use the discharge capability of these devices is it?  If not, what do you do with the unused pins.  I didn't see anything in the data sheet pertaining to this question. 

Additionally, if using the part to measure a string of 12V VRLA batteries, is there a problem using a resistor voltage divider to bring the nominal battery voltage to within the input range of the device?

Also, would anyone care to offer any advice regarding the monitoring of blocks or modules of parallel connected battery cells (say six cells), wherein these modules are then connected in series to create a string of modules (say 24 modules)?  In particular, the individual battery cells within the modules are unable to be monitored individually/interdependently.  Is this something that's done in certain EV applications?

I appreciate in advance any and all responses!

  • I am also interested to hear the answer to the unused pins question since the datasheet does not address it.

    Regarding paralleled cells, the cells will naturally balance to keep their terminal voltage equal. There is very little to no benefit in measuring (using separate sense lines and monitoring IC) the voltage of paralleled cells. I have not seen it done in the EV world.

  • 0
    •  Analog Employees 
    on Apr 28, 2020 1:15 PM

    Using BMS in this application is not possible with VRLA batteries. Cell voltages measured in BMS are differential. i.e. C(n) is measured w.r.t C(n-1) . In the given case achieving this wont be possible. You can probably use the resistor divider and measure it with an ADC.

    Also if you are also looking at balancing lead acid batteries please check LTC3305.

  • Thanks Abhishek,

    Yes, I see what you're saying as I looked more closely at my concept, my bad.  I'm wondering if I might be able to create the "string" of smaller attenuated differential voltages using an array of difference i.e. "funnel' amplifiers (AD8475, or AD8279) with their outputs referenced to the successive amplifier outputs; since the common mode voltage range allowed for these type of amplifiers is so large.  What do you think?  I really want to take advantage of the capabilities of the Multicell Battery Stack Monitoring ICs.  In my current system (almost 10 years old) we use an array of difference amplifiers to measure 12 series connected 2V batteries.  The 2V battery cells are no longer being made so we are upgrading to 12V batteries.  Any other schemes you might recommend?  Thanks so much.

  • For the funnel amplifier part, scratch the AD8475; I meant the LT1997-2.

  • 0
    •  Analog Employees 
    on Jul 10, 2020 9:43 AM in reply to Vicman

    Hi Vicman,

    If the absolute max conditions from the IC datasheet are met in all possible conditions then this is possible. Although there might be some tradeoff on accuracy as the application design is optimised for a string of cell lines.