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BQ25505: Can VSTOR be configured?

Jun Xian Low
Prodigy 100 points
Part Number: BQ25505

I found that VSTOR seems to have 4.2V as its max charging value, but is it adjustable and how? 

Thanks and appreciate your help.

  • 0
    TI__Guru**** 166866 points
    Jun,

    VSTOR max voltage is set using the VBAT_OV resistors, connected to RDIV. You can use www.ti.com/.../sluc484 to help size those resistors.
  • 0 in reply to Jeff F
    Prodigy 100 points

    So VBAT_OV basically determines the max VSTOR value, also the output at VOR. 

    I did an experiment, without adding or changing any resistance on the bq25505 module, I supplied total of 5.1V battery at the VBAT_SEC, the VSTOR value is suppose to be about 4.2V by default, but I measured and got the same value as the VBAT_SEC, 5.1V. Is this operation normal as the VBAT_SEC takes over the VSTOR and to the output VOR?

    Also, I have a few doubts do you mind answering me on that:

    1. If I connect a 5.1V battery at the VBAT_SEC, is the VSTOR which is getting input from VIN_DC able to charge up the battery? (since the voltage is higher on the VBAT_SEC)

        I would think that only when VBAT_SEC drops to below VSTOR (VBAT_OV), boost converter is enabled again giving input to VSTOR, and that input will BOTH supply to load VOR and charge up battery at VBAT_SEC at the SAME time, is this true?

    2. In the ratings, VIN_DC, VSTOR, VBAT_SEC all have 0.3 to 5.5V maximum ratings. If I want to give a 5.1V output at VOR, I will use 5.1V in VBAT_SEC and set VBAT_OV to 5.1V. Is this the right thing to do?

    Thanks! Appreciate your replies.

  • 0 in reply to Jun Xian Low
    TI__Guru**** 166866 points
    Jun,

    There is a PFET connecting VSTOR and VBAT_SEC, with its body diode always allowing current flow from VSTOR to VBAT_SEC. When VSTOR is above VBAT_OK threshold, the PFET turns on and connects VSTOR=VBAT_SEC. The output VOR will also be VBAT_SEC because VBAT_OK also controls the gate drivers that control the VOR external FETS.

    Regarding 1, yes. The boost converter stops switching if VBAT_SEC=VSTOR > VBAT_OV. When VSTOR<VBAT_OV, the boost converter turns back on and powers VSTOR which provides system load through VOR or charges VBAT_SEC.

    Regarding 2, yes.