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BQ2962: BQ2962: Could we let REG pin floating when NO use the RTC(LDO) feature

HY
Intellectual 1550 points
Part Number: BQ2962

Hi,
Our design no LDO requirement but we will leverage the current PCB.
So, could we let REG pin floating when NO use the RTC(LDO) feature?

  • 0
    TI__Guru 54715 points

    Hi HY,

    Since the BQ2962 does not have the regulator disable and a capacitor is needed for stability of the REG output you would need to install the capacitor even if the regulated output is not used.  Select the smallest capacitor size recommended since you won't have a load.

     

  • 0 in reply to WM5295
    TI__Intellectual 1550 points

    Hi,

    Thanks for your feedback. I have some questions that need your comments.

    A). Would we need a capacitor only or a capacitor with/series a resistor? 

    B). How much capacitance/resistance do you prefer? Give us the range that is good for various design in the future.

    C). Can we use 0.1uF for that?　Since 0.1uF is a popular capacitor for our design.

    D). The resistor is must stuff in that design even if no use regulator of REG. If so, do we use 100 ohm for that?

  • 0 in reply to HY
    TI__Guru 54715 points

    Hi HY,

    A. If you have the resistor on the layout and want to re-use the board without RTC, you would need the resistor also.  If you have the resistor to avoid inrush current which breaks the BQ2962 during random cell connection it should be retained.

    B. For the capacitor the minimum recommended CREG in table 9-1 is 0.47 uF.

    For the resistor data sheet section 9.2.2 suggests: ...a resistor of a minimum of 5 Ω to a maximum of 10 Ω

    C. The data sheet pin function table indicates REG "Requires an external ceramic capacitor for stability".  Since your design does not use the REG voltage you may not be concerned about ripple or settling time of the REG output.  I can see the attraction to 0.1 uF, and you might try it if you wish to see if there is any undesired effect in your design, but I would recommend staying with the minimum recommended value of 0.47 uF in table 9-1.

    D. The resistor limits the inrush current to the capacitor at cell connection.  It should not be too large that it isolates the regulator from the capacitor allowing instability.  The 5 to 10 ohm guidance of the data sheet is a good recommendation.