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BQ25570: Input source protection

user5845893
Intellectual 690 points
Part Number: BQ25570

Are any protection at the input site? What will happen when I give more power than 0.5W to device?

  • +1
    TI__Guru*** 143880 points

    Hi,

    Yes. The charger limits its input current to 220mA typical.  Since this is a boost charger, the input MPP voltage at VIN_DC must to be ~ 400mV below the VBAT_OV set voltage, which is max 5.5V.  If the input MPP voltage exceeds the VBAT_OV voltage, the charger turns on a pull down resistor at VIN_DC that is intended to pull down the HiZ source from overvoltaging the storage element.

    Regards,

    Jeff  

  • 0 in reply to Jeff F
    Intellectual 690 points

    Hi,

    okay thank you. I have own PCB with BQ25570. It is configured in that way:

    VBAT_OK_HYST = 3.167V
    VBAT_OK = 2.985V
    MPPT = 80%
    VBAT_OV = 3.630V
    VBAT_UV = 1.950V
    VOUT_SET = 3.030V

    For the test I use as a source bench power supply, I ramp the voltage from 0 to 4.4. I measure input and outout current and the measurements looks like this: 

    and when I go from 0V to 4.4 and back:

    The boost mode looks good, but afterward it looks like I can raising voltage and current also raise proportionally, and the input is not going into HiZ.

  • 0 in reply to user5845893
    TI__Guru*** 143880 points

    Hi,

    What is the voltage doing?  Is IOUT from VSTOR to a load?  Is the battery helping to supply the load to VSTOR?

    Regards,

    Jeff

  • 0 in reply to user5845893
    TI__Guru*** 143880 points

    To confirm, you have your battery connected at VOUT of the buck converter, presumably to charge it up faster and bypass cold start. Also, you have VSTOR pin shorted to VBAT pin and VBAT is not connected to VOUT?  

    If so then as long as VIN_DC < VBAT_OV and VSTOR>=2.0V, the boost converter should have a switching waveform at LBOOST and boost up the input voltage.  As you increase input power, either by increasing the voltage or increasing the power source current limit, the VSTOR voltage should increase but not rise above 3.603V.  The max output current from VSTOR=input current to buck converter can't exceed 1/2 of the peak current ~=110mA.  The buck converter VOUT pin should increase to 3.03V no max output current being 110mA.

    If VIN_DC>VBAT_OV, LBOOST stops switching and an internal FET pulls down the input voltage in an attempt to prevent the input voltage from over-voltaging the battery at VBAT through the internal PFET body diode.

     Regards,

    Jeff

  • 0 in reply to Jeff F
    Intellectual 690 points

    I have connected battery to VBAT that on my charts I named it as Vout.

    VSTOR is not connected to VBAT neither to VOUT. 

  • 0 in reply to user5845893
    TI__Guru*** 143880 points

    As long as the input current does not exceed 100mA average, the LBOOST pin is switching and VIN_DC<VBAT_OV, I don't see an issue here.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Intellectual 690 points

    Okay thank you, so when I will increase input voltage above VBAT_OV it will increase without limits? There is no input voltage that will be blocked?

  • +1 in reply to user5845893
    TI__Guru*** 143880 points

    Correct.  As shown in the block diagram, the internal high-side, boost converter PFET body diode provides a path from VIN_DC to VSTOR and then the internal UV protection PFET body diode provides a path from VSTOR to VBAT.  So, VBAT could be 2 body diode voltage drops from VIN_DC.  This is a boost only charger so VIN_DC must be below VBAT_OV.

    Regards,

    Jeff