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bq20z65 communication errors

Joe Perino
Intellectual 640 points
Other Parts Discussed in Thread: BQ20Z65

Hello,

We are using the bq20z65 for a simple 4s battery pack.  The design/layout for this simple battery is basically  right out of documentation provided by TI.  On the boards we just received, I notice a couple of problems that we have never experienced before and am wondering if somebody from TI can maybe point us in the right direction to determine the cause and find a solution.

When we are charging the battery (3A ~ 1C) we notice communication dropouts on the SMBus.  The only other irregularity we notice is that 2.5V reference output from the bq20z65 is 2.65V when not charging, and increases to about 2.75V when charge current is in the sense resistor. 

As mentioned, the layout guidelines were followed, do not see any component errors on the board.  Just looking for some ideas as to where to look for cause/resolution.

Thanks,

Joe P.  

  • 0
    TI__Guru* 76230 points

    Hi Joe,

    How frequent are these communication drop outs?

    DS has the max for the 2.5 LDO as 2.59 V. 2.65V clearly is an anomaly. Is this problem repeatable across several boards. Have you tried replacing the IC on your board? Can you check to make sure you have the right cap values on RBI and Reg pins?

    thanks

    Onyx

  • 0 in reply to Onyx Ahiakwo
    Intellectual 640 points

    Hello Onyx,

    I have observed that the communication dropouts are infrequent with low or no current (every 10s or so), but are very frequent with charge current.  I see both NACK and T2H (clocking) errors.  They are present on every board.

    I have not been able to determine why the 2.5V is not clean and in line with the DS.  I have checked VCC, VSS, and the 3.3 and they all look fine.  There is a 4Hz oscillation riding on top of the 2.5Vreg.  I have checked that caps are present on RBI and Reg but will recheck the values. 

    Thanks,

    Joe P.