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bq20z45 current drawn when should be shutdown.

ken thompson
Intellectual 630 points
Other Parts Discussed in Thread: CSD, BQ20Z45

We have some interest in preserving cells in a pack that has been discharged and left for a bit of time.  We discharged a pack of three LIFePo cells, that has one low capacity cell.  After hitting the 2v limit on one cell, the pack was disconnected from SystemPresent and from the SMBus.  Once an hour it was checked by connecting the SMBus.  First why does a pack not go into shutdown with very low current draw in this state?  Why, when the poor cell gets to 2v (our cell shutdown voltage) does the current draw INCREASE until the cell is cratered?  I have a chart showing the current increase below programmed shutdown threshold.

K12-10155 TI GG discharge.xls
  • 0
    TI__Guru 73830 points

    Ken, 

    Your pack should have reached CUV and opened the discharge FET and there should not be any discharge current. Are there any Permanent  Faults? The pack will not transition into Shutdown, if PF's are present. Do you have the SHUTV bit set in the Operation Cfg C register? I can review your gg file and the chart showing the current increase, if you want to forward them.
    Regards
    Tom

  • 0 in reply to ThomasCosby
    Intellectual 630 points

    Thanks Thomas.  here is my .DFI file.  My guide to using this part has always been sula404 Application Book for bq20zxx.  SHUTV is never mentioned in it.  How are we expected to use a part with incomplete documentation?

    Or not.  .DFI files not allowed?

    Only known URLs and the following file extensions are allowed: 123, 7z, aac, ai, aiff, art, asf, asx, avi, bmp, config, csd, css, db, db, dmg, doc, docx, drw, eml, flac, flv, gif, gz, htm, html, ics, jpeg, jpg, log, m4a, m4p, m4v, mdb, mdbx, mid, midi, mmv, mov, mp3, mp4, mpg, mpp, msg, ogg, pdf, png, pps, ppt, pptx, ps, psd, qt, ram, rar, rm, rtf, sit, sitx, sql, swf, tif, tiff, txt, vcf, vcs, wav, wma, wmv, wpd, wps, xls, xlsx, xml, zip, tsc, tsm, ibs, diff, tar, tar.gz, gel, ccs, cpp, asm, sa, c, cc, sch, ini, cfg, cxx, s, asm, pjt, vsd, sch, pcb, lib, cir, mcd, xmcdz, xmct, jmp, jsl, dat, brd, vsm, h, usb. Please select a valid file or enter a valid URL.

    Here is the .gg    OR NOT.   zip file?  OK that took....

    Ken.

    302.zip
  • 0 in reply to ken thompson
    TI__Guru 73830 points

    Ken,

    I reviewed your .gg file and loaded the .dfi file into my EVM and tested Shutdown. I observed the same results that you reported. SHUTV is set to "0" in the Operation Cfg C register and this sets the Shutdown qualifier to used the Pack Shutdown Voltage. I set this bit to "1" and retested the pack by lowering one cell voltage and the pack does go into Shutdown at a 2.1V cell voltage. (The Cell Shutdown Voltage is set to 2100mV in your dfi file, where it is set to 2000 mV in the gg file.) You do not have to remove the SMBus to allow the device to go into Shutdown.

    The SHUTV bit is discussed on pages 44 and 141 of the bq20z45 TRM. You should use the device Datasheet and Technical Reference Manual as the official documents to setup a device. The Applications Book covers a lot of general material that it not covered in each device specific documents, but it does not cover all of the detailed information. 

    I hope that this helps.

    Regards

    Tom