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BQ76940EVM: Operating voltage

Genius 9880 points
Part Number: BQ76940EVM
Other Parts Discussed in Thread: BQ76940

Hi Team,

Good day.

Customer have following confirmation about our bq76940EVM. 

1. When Simulating a battery of 9 cells on the bq76940EVM, what is the minimum operating voltage?

2. What is the minimum value of the cells before the BQ76940 is no longer operational - when BATT+ and BATT- are powered by the cells?

3. Also, at what point does the BQ76940EVM, in its default state, determine a cell is operating at overvoltage or undervoltage?

Regards,

Maynard

  • Hi Maynard,

    1. The minimum operating voltage stated in the BQ76940EVM User Guide Table 2. Performance Specification Summary is 38V.   The minimum recommended operating voltage for the BQ76940 VBAT (cell group power supply) is 6V or 18V total.  The minimum recommended for the REGSRC input is also 6V.  On the BQ76940 EVM the REGSRC is derived from VC5X and is likely about 3V below the VC5X (VBAT) so it likely meets minimum recommended operating conditions for the part with a VBAT (cell group power supply) voltage of about 9V or a BATT+ voltage of about 27V.  The 6V on REGSRC should run the REGOUT regulator ok but does not give a lot of voltage for the FET gates.

    2. The reset level of the BQ76940 is VSHUT, again for the cell group power supply voltage VBAT, 3.6V maximum, or 10.8V for BATT+ if all groups match.  However REGSRC would have fallen to near 1V at that voltage and REGOUT would not be sufficient to operate the part.  If you alter the board to provide a higher REGSRC it should operate to this level if the cells match.

    3. The EVM has the default states of the BQ76940, OV and UV are set at ADC values, OV at 0x2AC8, UV at 0x1970. See the data sheet section 10.3.1.2.1 Integrated Hardware Protections.  Since each part has stored gain and offset for the cells, the voltage may vary slightly for each device.  Below the UVMINQUAL a cell is considered shorted and will not trigger UV.