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BQ76940: Abnormal Readings at the AFE pins VC5 to VC10

rohsik_j
Prodigy 165 points
Part Number: BQ76940

Hello,

We are working on AFE BQ7694001 with companion IC 14Sseries. Please find the attachment for the schematic.

we are facing a suitation where at voltage reading at the pins with IC and without IC are as follows mentioned in the table.

VC0

VC1

VC2

VC3

VC4

VC5

VC5B

VC6

VC7

VC8

VC9

VC10

VC10B

VC11

VC12

VC13

VC14

VC15

With IC

0

3.8

7.6

11.5

15.3

19.1

19.1

22.9

27

31

35

39

39

43

47.1

51.1

51.1

55.2

Without IC voltage at pads

0

3.8

7.67

11.5

15.3

19.25

28.26

28.28

28.3

30.8

30.6

30.02

38.1

42.1

47

51.1

51.1

55.1

Afer the IC is placed the Voltage measured by multimeter wrt ground from VC5B to VC10B is abnormal.

Also after When the IC is being soldered R51,R45 and R52 is starting to bleed.

Kindly review the schematic and let us know what are we missing, else what might be the cause os abnormal voltage readings.

Note: If IC is removed then the Voltages at the Pads are showing normal readings

file602B9B3A-BMS_AFE.pdf

Thanks in Advance

  • 0
    TI__Guru 54715 points

    Hi Rohsik,

    From the description I wonder if the labels for the table rows might be swapped.  The first row would seem to be cell voltages applied with the cells about 4V each.  VC5 and VC5B are the same since there might be no attached circuit.  The second row looks like all the pins of the middle group are approximately shorted together.  I would wonder if the IC may be damaged with a low resistance between VC10X and VC5X.  If the IC is still mounted you might connect the supply/cells and check the voltage across R56 and R57.  Similar voltages with opposite signs would indicate current into VC10X and out VC5X, possibly from a damaged IC or short under the IC.  The VC5B through VC10 would be approximately pulled together between or near the voltages of VC10X and VC5X.

    Measuring VC10X and VC5X wrt ground may also be informative.

    With the VC5B to VC10 pulling toward a common voltage Q15 and Q13 are likely to be off, Q16, Q14, and Q17 are likely to be on.  This is the probable cause of the current in R51, R45, and R52.

    Unless you find a short under the IC it is likely that the BQ76940 has been damaged.