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BQ25570: MAX Charging current at 4.2V

Ajay Kumar
Prodigy 45 points
Part Number: BQ25570

Hello,

I am using BQ25570 for Solar Battery charging circuit. I came across datasheet in that i find IC can provide maximum charging current of 110mA.

I like to know max current that IC can provide at 4.2V. 

  • 0
    TI__Guru**** 167196 points

    Ajay,

    The boost converter operates in discontinuous PFM with peak inductor current of about 220mA therefore the absolute maximum possible output current is 1/2 the peak inductor current or 110mA . For this to happen, you would need a low impedance power source (for example, likely not a solar panel) at VIN_DC that provides very close to but still less than VBAT_OV .   As with all boost converters, you can estimate maximum output power using a power balance where efficiency = Pout/Pin = VSTOR*ISTOR/(VIN*IIN_AVG), efficiency can be predicted from the datasheet efficiency curves.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Prodigy 45 points

    Thank you Jeff,

    For your reference

    I selected BQ25570 for my application because below mentioned Feature of IC.

    "The product is specifically designed to efficiently acquire and manage the microwatts (μW) to miliwatts (mW) of power generated from a variety of high output impedance (HiZ) DC sources like photovoltaic (solar) or thermal electric generators and a piezoelectric generator."

    Also HiZ DC sources maximum output power point was track by MPPT setting to transferring the maximum amount of power currently available per ambient conditions to the output.

    Need a clarification regarding below point.

    In Absolute Maximum Rating of BQ25570 "Peak Input Power, PIN_PK = 510 mW". So for VIn = 4.2 V max input current will be 121 mA and with 93 % of efficiency I calculate maximum charging current as 113mA. i think to get 280mA input voltage must be around 1.8V.

    From Datasheet:

    Cycle-by-cycle current limit of charger         Typical = 230 Maximum = 285 mA

    (0.5V < VIN < 4.0 V; VSTOR= 4.2 V  )     

    Kindly do the needful.

    Thank you.

  • 0 in reply to Ajay Kumar
    TI__Guru**** 167196 points

    Ajay,

    I do not understand your question.  How can Vin=4.2V max but then input voltage be 1.8V? 

    Regardless, the max input power is from max Vin * max average input current.  So, the datasheet is under-estimating slightly.  Wtih Vinmax=5.1V and max average input current = cycle by cycle current limit=285mA times 50% switch duty cycle, the max theoretical power is 5.1V*0.5*285mA = 0.727W.  You will likely only be able to reach this in a lab condition with a unit that has cycle by cycle = 285mA and with the Vin-dc to VSTOR boost duty cycle is 50%.   A more realistic maximum, using the typical cycle by cycle limit is 5.1V*0.5*230mA =.587W.  But again, you would need to be at duty cycle = 50%, as set by the Vin-dc to VSTOR difference and a low impedance source.  

    Regards,

    Jeff