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Bq25504 /5 Li-ion charging current limit.

Ori Yulzary
Prodigy 50 points
Other Parts Discussed in Thread: BQ25504, BQ25505

I'm start evaluating the BQ25504 EVM connect to IXYS solar panel to charge Li-ion 100mA 3.7V battery for an outdoor detecror.

How can I limit the charging current to 0.2C?

Thank you

Ori

  • 0
    TI__Guru**** 166486 points

    The bq25504 does not control charging current.  The assumption is that the energy harvesting source is sized to provide just enough input power for the system load with the excess current going to the battery.

  • 0 in reply to Jeff F
    Prodigy 50 points

    Hello Jeff

    Thank you, for your rapid response.

    I wonder, how can I insure that the Li-ion batterty get the right charge profile (first constant current, then constat volatge and so on...)

    Can you please tell what the maximum current I can draw from VSTOR there is any diffrent between BQ25505 and BQ25504.

    What the recommanded batterty Size? 3.7V 100mAh is it OK?

    Thank you

    Ori

  • 0 in reply to Ori Yulzary
    TI__Guru**** 166486 points

    Since this is a boost converter based charger, the maximum output current is a function of input power.  You will have to use the following equation to compute the maximum output current:

    POUT/PIN = efficiency = (VSTOR*ISTOR) / (VIN*IIN) solved for ISTOR.

    You can get an estimate of efficiency from the datasheet efficiency curves.  VIN is MPPT set point.

  • 0 in reply to Jeff F
    Prodigy 50 points

    Hi Jeff

    Can you please tell what the maximun current I can get form STOR when running on battery (SEC_BAT), what is current limit of the internal switch?

    Thansk

    Ori

  • 0 in reply to Ori Yulzary
    TI__Guru**** 166486 points

    There is no active current limit on the switch between BAT_SEC and VSTOR.  The switch's RDSon will practically limit the amount of power from the battery by causing a voltage drop from BAT_SEC to VSTOR for large current flows.

  • 0 in reply to Jeff F
    Prodigy 50 points

    Thank you,

    Do you have solution for NiHM battery charger form solar source with the BQ25505?

    Why in BQ25504 HiHM is mentioned while in BQ25505 it does not?

    Ori

  • 0 in reply to Ori Yulzary
    TI__Guru**** 166486 points

    To keep the bq25504 and bq25505 quiescent current low, current regulation circuitry and temperature sensing circuitry was not added.  The bq25504 and bq25505 only prevent over discharge and over voltage.  In addition, with high impedance sources providing power to the low power bq25504 and bq25505 chargers, the output power from these chargers will be low and will likely come in bursts instead of steady current over a long period of time.  The likelihood of damage to a LiIon or NiMH battery with this derivative of traditional "pulse charging" is very low.