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BQ76940: questions

Ivy Jin
Expert 4595 points
Part Number: BQ76940
Other Parts Discussed in Thread: BQ76930

Hi team,

My customer is evaluating BQ769X0 in their project.

Below are some questions, could you please help to give some comments? Thank you.

1. Why did cell 10 and cell 15 of BQ769X0 read data on the evaluation software that was 5mV lower than the actually measured voltage, and others cell voltage are normal?

2.Why does the Coulomb counter with BQ769X0 be enabled with more power consumption than the Coulomb counter with disabled?

3. Before and after the BQ76930 package is heated by the customer’s soldering iron, the measurement of cell voltage varies significantly.

Before heating

After heating

Appreciate your help!

Thank you.

Regards.

Ivy

  • 0
    TI__Guru 54715 points

    Hi Ivy,

    1. In your specific case I don't know.  Possibilities may include part to part variation, or use of Schottky diodes between the top group input and power pin as shown in figure 14 of the data sheet https://www.ti.com/document-viewer/BQ76940/datasheet/typical-applications-slusbk29872#slusbk29872 instead of conventional diodes.  With a shorted thermistor  the added load on the supply pins in addition to the ICC_BAT or dINOM current may forward bias a Schottky diode.  Check for unexpected voltage drop across the resistors for VC5, VC10 and VC15.  Note that the top input of the group does have higher current than the other inputs, but the dICELL max of 0.5 uA should give 0.5 mV across the typical 1k filter resistor, not the 5 mV reported.

    2. The CC enabled runs more circuitry in the part than when the CC is disabled, so current is higher when enabled.

    3. There can be a temperature coefficient of the ADC.  The part can also be subjected to stress during mounting which can be relieved by reflow. The voltages after heating seem much more consistent.  Optimize the board assembly process to avoid stress on the part.