BQ76930: Issue on first cell voltage with BQ7693003DBT

Hi Gopal,

It looks like the cell balancing FETs are upside down. The source should be facing the resistors and the higher voltage, the drain should be facing the lower voltage. As they are now they would be allowing the cells to balance all the time. I'm not sure if this is the root cause, but it is definitely something that needs to be fixed.

Regards,

Max Verboncoeur

Actively now i a not added any external cell balance components only added 1K and 0.22Uf capacitors only 

Actively now i a not added any external cell balance components only added 1K and 0.22Uf capacitors only 

Present  we are using this one check it any changes , still not getting cell1 voltage

Hi Gopal,

Could you try measuring the voltage at the VC1 pin (VC1-VSS) and VC0 pin (VC0-VSS)?

Is the boot switch being held down?

Regards,

Max Verboncoeur

Thank you for replaying,

BQ7693003 output:

cell1 -3693

cell2 -4108

cell3 -4077

cell4 -4085

VC0-VSS -  .412V

VC1-VSS -  4.250V

and we are using boot switch to turn on the bms ic only , not directly connected to CELL1

Hi Gopal,

VC0 should be close to VSS. The device measures VC1-VC0 to get the cell 1 measurement. Is the device VSS not connected to VC0 trace through the battery negative terminal? See the highlighted path for an example:

Through this path, VC0 should be near 0V. Could you check if your system has this path?

Regards,

Max Verboncoeur

No, we need isolated ground which is why we are not connected to VSS and VC0. we checked the connection VC0 and GND with 1k resister, shorted also, not working value shot same no change on  Voltage 

and i an using this to refers www.ti.com/.../TIDA-00449

.

We are using this reference in the circuit 

in our circuit, we observed one more thing , when BMS ic is started Cell 1 voltage is fine(4.021) after 1 sec the voltage slowly down to 3.693V

we replaced all 1K -100 Ohms, 0.22UF -1UF. then we are getting  Cell1-3.8 (4.025 real value), than change the R38 - 1ohm and R41- 10Ohm than we are   getting near value for cell voltages. But not stable voltage  

    Cell1- 3.982(4.032 Real )

   Cell2- 4.025(4.045 Real )

Any update on this ???

1. Can please check my circuit diagram  and any changes required or any modifications 

Hi Gopal,

The device measures VC1-VC0 to get the Cell 1 voltage value. I expect the reason that the measurement starts out okay is because the capacitor (C22) is near 0V so VC0 is close to VSS. When the device takes a measurement, it pulls a small amount of current into the pin, and this likely charges the capacitor over time, resulting in a worsening measurement.

Do note that the TIDA you mentioned has VSS connected to the battery negative (VC0) through the below portion:

Could you check your connections and make sure that VC0 is correctly connected to VSS?

Regards,

Max Verboncoeur

Yes , but I am not connecting to VC0 TO VSS , with out connect VSS,VC0 the cell voltages will not come correct???

And I try to short the VC0 and VSS,than I will know . And in my application  i need to isolation of ground required. IF MOSFET is off than allso form I2c ground is still load is ON .

give the suggestion circuit for 10s with ba76930 30a with ground isolation circuit.

Thank you Maxwell