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Configure VTI problem with advanced bqmtester on a 3 cell board

Dennis Kindschuh
Prodigy 180 points
Other Parts Discussed in Thread: BQMTESTER, BQ29330
I am working with an HPA495 Advanced bqmtester.  
For the most part it is all working.  But I have a problem when trying to 
calibrate the VTI.  It may simply be how I wired it up.  
> 
> My board is a three cell,  BQ2933/BQ20x70-V160 circuit.  I have Cell 1 - (from 
the HPA495) to the minus end of the bottom cell connection, on my board.  Cell 1 
+ to the positive of the bottom cell.  Cell 2 + to the positive of the next 
cell, and Cell 3 + to the next one.  I have cell 4 + not connected to anything.  
In setup I have told it we are a 3 cell.  If I run the "Configure VTI" in the 
main program without connecting the Pack + connection to my board,  I see a 
nice, stable set of voltages.  Cell1- to + is 3.718.  Cell 1 + to Cell 2 + is 
3.645.  Cell 2 + to Cell 3 + is 3.683.  Cell 1 - to Pack + is 14.2.  That seems 
to be the problem, because when I connect Pack + to my circuit, Cell 2 + to Cell 
3 + goes up to over 4 volts, and is not stable.  Should I be doing something 
with the Cell 4 + connection?  I thought it would  take care of itself in setup, 
when I told it I was a 3 cell.  
I did see a post asking something similar and the answer was to connect the Cell 3 + to the Cell 4 +.  When I   tried that, the voltage between Cell 2 + and Cell 3 + went to 7.8 v.  The total stayed at 14.2 or so.
>
  • 0
    TI__Guru* 76230 points

    Hi Dennis,

    Have you looked at the user guide for the bqMtester? Did you place the jumpers as described on page 23 of the user guide?

     

    thanks

    Onyx

  • 0 in reply to Onyx Ahiakwo
    Prodigy 180 points

    Hello Onyx

    I am using the HPA495 Advanced bqmtester.  I think you are looking at the HP169 bqmtester.  I see the jumpers on that board, but no jumpers on the HPA495.  Am I missing something?  Jumpers would be nice.

    dpk

  • 0 in reply to Dennis Kindschuh
    TI__Guru* 76230 points

    Hi Dpk,

    That was an oversight missing the fact you are using the "advanced" bqmtester and not the other as I thought.  On your board, you will have to short 3p and 4p, while on the advanced bqmtester board, you will need to keep the 4p pin floating. Let me know if this helps.

    thanks

    Onyx

  • 0 in reply to Onyx Ahiakwo
    Prodigy 180 points

    Hello Onyx

    I apologize if I am still missing something.  If you check my first posting, you will see that I have the Advanced bqmtester 4P (Cell4+) floating as you suggest . My board is a 3 cell, so it does not have a 4P(Cell4+).  If I do not attach the Pack+ from the Advanced bqtester to my board, all voltages look correct on Cell1-,Cell1+,Cell2+ And Cell3+.  The voltage at Pack+ is 14.2 vdc.  The problem occurs as soon as I attach the Pack+ to my boards Pack+, the voltage at Cell3+ goes up and becomes unstable.  

    dpk

  • 0 in reply to Dennis Kindschuh
    Prodigy 180 points

    Hello again Onyx

    One thing that i should add is that my board is a mature board.  That is, we have built and shipped several hundred.  It programs, calibrates and tests good using the bqeasy.  Its just that the Advanced bqmtester would make it go so much easier.  The design is nothing unusual.  It was taken directly from the TI ap note.

    dpk

  • 0 in reply to Dennis Kindschuh
    TI__Guru* 76230 points

    HI Dpk,

    I understand you have a 3s cell, but on the schematic of your board, for your 4th cell, is the pin floating or tied to pin 3p/ i.e is 3p tied to 4p on your schematic?

    thanks

    Onyx

  • 0 in reply to Onyx Ahiakwo
    Prodigy 180 points

    Hi Onyz

    The pins VC1 and VC2 are tied together at the bq29330. That point is tied to the top of the Cell3 through a 100 ohm resistor.

    dpk

  • 0 in reply to Dennis Kindschuh
    TI__Guru* 76230 points

    Hi Dpk,

    Do you have a schematic you can share? In the meanwhile, I will obtain the advanced tester and hook up my EVM to it to see if I see similar issues. Did you say your calibration works fine using EVSW?

    thanks

    Onyx

  • 0 in reply to Onyx Ahiakwo
    Prodigy 180 points

    Sure thing Onyx.  I can send the entire package to you.  What is your email?

    Everything works with the lash up using the bqeasy.  3 resistors simulating the cells.  The advanced bqtester also works.  As I said, I can start the "configure VTI" and measure my cell pack voltage.  With the Pack+ not connected I see 11.046 volts and with it connected I see an unstable 11.970 volts.  I can enter either value in the Total V spot.  Also the 500ma current is good and the temp is good, so I click "Update VTI and Close".  Then I click START and the bqtester programs and calibrates just fine.  So everything works as expected.  I am only concerned because of the voltage I see during "configure VTI" with the Pack+ connected.  

    dpk

  • 0 in reply to Dennis Kindschuh
    Prodigy 180 points

    Hello Again

    Since I had not received a response, I chose to simply "configure VTI" without the Pack+ connected, then run the calibrations with it attached.  This seems to work OK.

    I do have a new question.  I also am making a board  using the bq27541DRZT-V200.  We have now built around 1K and are going to run another 3K next week.  Referring to the reference schematic on page 36.  What would be considered the acceptable capacitance range for C1,C2,C4,C5 and C7?  This application is a very tight fit.  I am having a hard time finding 0.1mfd thin enough to clear.  Oddly, I have found 1000pf and 0.47 mfd  in thin enough packages. Also, when I made the board, I did not put a place for C11 and C12.  What are the possible consequences?

    thanks

    dpk

  • 0 in reply to Dennis Kindschuh
    TI__Guru* 76230 points

    Hi Dennis,

    My apologies as it seems I missed your last post. Good that you found a work around for your issue. The bq2754 is supported by a different group since it is a single cell gas guage. I suggest starting an entirely new post with the IC name as the subject so the appropriate group can respond to it.

    thanks

    Onyx