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bq77PL900EVM UV & OV Problems

Michael Bell
Prodigy 20 points
Other Parts Discussed in Thread: BQ77PL900

Hi there -

I'm using the BQ77PL900 Evaluation Module and having some issues. I have everything connected seemingly correctly and using the evaluation software to see the register values. The module is not outputting anything, when in host mode and CHG/DSG are selected they do not get activated. The cause of this seems to be from the UV and OV status registers being high, something which I have not been able to figure out why. I have tried a variety of different input setups. I tried from 5-10S 3.7v cells to no avail. I've tried a variable power supply on the input with 160ohm resistors to voltage divide down with sweeping input voltages also to no avail. I am able to power the chip on (obviously if I can see the status on the software), but there has been no apparent reason for OV/UV to be high. Each time I have changed input configurations I changed the appropriate CNF#. 

I have also tried standalone mode, but there is simply no output and not much else I can do to debug in that mode. After fooling around with input configurations I decided to program the EEPROM in case the OV/UV configurations that came with the evaluations module were massively screwed up. I programmed it with the settings shown in the attached picture but the UV/OV status's have not changed.

Any suggestions as to what is the issue? Did I just receive a DOA chip/evaluation module? 

  • 0
    TI__Guru 54715 points

    The part is showing you it has a simultaneous OV and UV.  Most likely the differential pin voltage of one cell is low at the IC, since it shows up with as few as 5 cells, likely between one of the pin pairs between VC6 and VC11.  You will likely find the voltage between one pin pair is significantly lower than your cell voltage and one or both of the adjacent pin pairs is high causing the simultaneous OV and UV. If you are fortunate, there will be some contamination on the board or it is sitting on something conductive. Check also that the terminal block inputs areconnected to the wire and not its insulation thus allowing an input to be pulled down by sampling as the part operates. Check the Rvcx input resistors on the bottom of the board for damage to the components or solder.

    Your input connection scheme must be planned to prevent exceeding the absolute maximum pin voltages during connection. The recommended bottom up cell connection sequence should avoid that and the large capacitance on the output of the EVM should keep the device from starting up before the PACK side voltage is intentionally applied.  If you miss an input the capacitor divider on the input pins should distribute the voltage.  Once the missing input is probed or sampled by waking up the device, it may be pulled to a damaging voltage.  If multiple sequential inputs are open, the damaging voltage potential is greater. If a cell input is damaged, typically there will be a large positive voltage across the upper Rvcx and a similar negative voltage across the lower Rvcx for that cell.

    The boards are tested after manufacture and believed good when shipped. Please check your setup using the suggestions above to identify the fault or damage and review your operations.  If the board is damaged, please contact your TI sales representative.

  • 0
    Prodigy 40 points

    Did you ever solve this?  I am having the same problem and so far haven't been able to figure it out.  I made sure that my voltage divider inputs were set up correctly, and I made sure that the voltage difference between pairs on inputs was right around 3V.  My board was working fine for a couple of days and then all of the sudden I had both an OV and an UV fault.  After checking that all of the inputs were correct, I replaced the IC because the board was kind of old and someone else used it before me so I thought maybe something had happened to the chip.  The new IC worked just fine for another couple of days until the same thing happened?

    I get the OV and UV faults immediately after starting the board up.  Even after I powered the whole thing down in hopes of resetting it, I get the same errors when I restart it.   Have you found anything that worked for you, or do I need to replace the IC again and just be really careful with it?  Thanks.

  • 0 in reply to E_Pinter
    Prodigy 20 points

    Sorry for the delay in responding. I haven't been able to get the board working. I tried all the steps to fix it, but the OV/UV fault is still there. I guess I'll try and get the board replaced, did you get an entire development board or just the IC?