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Just another newbie question

Jerome Girard
Prodigy 10 points
Other Parts Discussed in Thread: BQ24753, UC3906, BQ2031

Hello,

I want to build a charger for a VRLA battery based on a bq24753 and a PSoC.

I read the bq24753 datasheet and I don't find how I can set the charge voltage to the requirements of my battery (14.4V bulk charge voltage).

If I have understood, the Vbatt equation as some "discontinuities".

Thanks in advance

  • 0
    TI__Prodigy 720 points

    VRLA is lead-acid battery.

    Please use uc3906, uc3909 and bq2031 for lead-acid battery charger.

    bq24753 is for Li-Ion battery, the voltage range is for 4-4.512V/cell, so 14.4V is not in the range.

    If you set bq24753 for 2cell, then Vbat range is 8-9.024V, 3cell range is 12-13.536V, 4cell range is 16-18.048V.

    By using external opamp, you can fool the IC to other voltage as long as BAT pin see the correct votlage range.

     

  • 0 in reply to Mao Ye35
    Prodigy 80 points

    I am considering the bq2031 for an SLA charger for use  in a standby power application. 

    The device will be used outdoors so temperature-related behavior is important.  The datasheet indicates operating temperature (Topr) of -20 to +70C and "Temperature Under Bias" (Tbias) as -40 to +85C.  My application will only charge the battery when ambient temperature is -20 to +45C, but I need the charger to tolerate (not charge, but not fail) while ambient temperatures range from -40 to +85C.

    Can you explain the difference between Topr (-20 to +70C) and Tbias (-40 to +85C) for this part?

    See page 11 of the datasheet:

    http://focus.ti.com/lit/ds/symlink/bq2031.pdf

     

    Thank you!

  • 0 in reply to David Albert38351
    TI__Mastermind 31120 points

    Typically ICs are specified as maximum junction temperature (150C) and storage temperature range.  The ambient temperature operational range is not some magical temperature range where the IC no longer works, it is where the electrical specification range min/max is define.  For battery chargers, the range is often chosen much tighter than the process allows to show better specs.  Why spec a IC for a range where it is not typically used and push out the limits.  Most all silicon processes are validated for -40 to 150C, so when a IC is made in a certain process, the device components will work over that range, but the specific IC limits are set to according to characterization of the specific IC.  Your IC is specified for -20 to +70, which you are within the specified range, and is well within the process temperature range.  The spec is probably indicating that for a battery temperature range -40 to +85, the TS bias over this temperature range was characterized.