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BQ24450: Battery charging current not more than 500mA

Prashant Chavan6
Intellectual 320 points
Part Number: BQ24450

Hi All,

I have designed Charging ckt. for lead acid battery of 24V, 7.2A rating, and maximum charging current(Imax-chg) is 2.5A .

The problem is getting current not more than 500mA, headroom for input voltage is also not an issue, Input voltage is 4V more than output voltage. What i expect is battery should charge with current of 2.5A.

I have attached schematic of my designed circuit please go through it, and correct me if i was wrong somewhere, any help will greatly appreciated.

And one more problem is about measuring voltage of STAT1 pin, while mode change. is that voltage range mentioned in datasheet of bq24450??

Hoping reply ASAP!!!

Thanks,

Prashant C

sch of bq24450.PDF

  • 0
    TI__Guru* 75656 points
    The system is only delivering 500mA but is designed for 2.5A, somethings to look at:
    1.) This circuit will regulate voltage between Pin 5 IN and Pin 4 IFB to 250mV, check if this is the voltage you are seeing.
    2.) The R-sense resistor value is pretty low at 0.1 ohms and additional resistance in traces connecting the sense lines to the resistor could add additional resistance.
    3.) This design will require a large external supply in the 40W to 60W range, noise out of the supply is a possibility. Check with a scope and add bulk filter capacitors if needed.
    4.) Input power connections could be dropping voltage as the power connection come on the board. Check for higher than expected voltage drop at that point.
    5.) PCB design should have large traces for the power path, input power to R-sense to pass transistor and on to battery connection.