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BQ76940EVM: BQ76940EVM

Joao Paulo Teixeira
Intellectual 370 points
Part Number: BQ76940EVM
Other Parts Discussed in Thread: BQ76940, TIDA-00449

Hello,

1) About the power consumption.. the BQ76940 divides the cells in groups, do it causes an imbalance of cell of different groups?

For example if the Alert pin is set it will cause a higher consumption from the bottom group.. are there other conditions that may cause this imbalance? Is it relevant?

2)Is there a way to turn off the BQ76940?

3)Whats the maximum current that the REGOUT can supply?

4) During charging if balancing and adc are enabled bq76940 handles this automatically, or the host that has to stop the balancing read the adc and then return the balancing?

Thank you

  • 0
    TI__Expert 6085 points

    (1) All of the modes currents specifications are given in  EC Table.  The REGSRC currents  *DOES NOT* include currents for external loads attached to the REGOUT or I2C  comm. lines.

    (2) Bq76940 cannot be completely turned OFF. But be commanded to SLEEP (SHIPMODE) via the 2 registers (SHUT_A, SHUT_B) writes. Once in this mode, the part will need an external WAKE pulse( >1V on the TS1 pin).

    (3) REGOUT is specified to 10mA for proper regulation

    (4) There is NO built-in Balancing algo for the bq769x0 family. User needs to provide the algo to the host and the host loads the CB registers. Please down load the SLAU775 application note from the www.ti.com bq76940 product folder for the ADC and Cell balancing operations. A good example of the passive cell balancing scheme ( 150mA @42V) is provided in the TIDA-00449. The scheme addresses balancing as often as possible(a0 at end of the charge when the cells reach ~4V or higher (b) when the pack is in IDLE for > 30 min and the cell voltage is higher than 3.3V.

    hope this helps you in the school projects. Good luck

  • 0 in reply to Vish Nadarajah
    Intellectual 370 points
    Isn't there a way to increase the REGOUT current because the host I intend to use need more current?

    Thaks!
  • 0 in reply to Joao Paulo Teixeira
    TI__Expert 4640 points
    What is the current that is needed for your micro? We don't recommend higher than what is in the datasheet but it could perhaps run as high as 20mA max
  • 0 in reply to Joao Paulo Teixeira
    TI__Expert 6085 points
    LDO are not unlimited current source. Its actually sourced by RESGSRC in this device. The Line load regulation at 100mV is specified with a 10mA load. Now, If you want to disrespect the line regulation, you can pull-up to 20mA as a constant current. Typical micro do not consume about 3-5mA.
  • 0 in reply to Vish Nadarajah
    Intellectual 370 points
    1) I'd like to know if the BQ76940 consumes more current from the bottom cell group than the upper cells, beacuse I read that the alert pin supply comes from the bottom group then I should clean it as fast as possible to decrease this umbalance.

    2) OK.

    3) 10mA is to low for me but ok, thats what I needed to know.

    4) I've read the application notes and I've understood that when the balance and the adc are on the balance time is about 70% and the other 30% is for adc reading, but is done automatically by the BQ76940 schedule...
    For example, both adc and balance are on.. so the host doesn't need to turn the balance off to read the adc and then back the balance on again, because it's automaticaly done by the BQ76940. Could you confirm it?

    Thanks!!!
  • 0 in reply to Joao Paulo Teixeira
    TI__Expert 6085 points

    If the host is programmed to TURN OFF the ADC, then prior to cell balance(CB)the  Host also needs to TURN ON the ADC.Turning ON the CB does not automatically TURN ON ADC.

  • 0 in reply to Vish Nadarajah
    Intellectual 370 points
    Let's suppose that the host turned on ADC and CB, if the host get the adc readings it will return a wrong value due to the cell balancing?
  • 0 in reply to Joao Paulo Teixeira
    TI__Expert 4640 points
    www.ti.com/.../slua775.pdf

    This appnote should explain what you want to know. The short answer is the scheduler will not allow an ADC reading at the same time that it balances.
  • 0 in reply to Miguel Angel Rios
    Intellectual 370 points
    That's what I needed to know, I've already tested what I was asking and confirmed that if cell balance is on and adc is enabled the bq76940 will automatically turn off CB for a period of time to read all adc and then turn CB on again

    Thanks