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Original question:

BQ25505: BQ25505 is not Working without solar when connected Battery?

BQ25505: Battery disconnected when no input

Giovanni Gherardi2
Prodigy 20 points
Part Number: BQ25505

Dear All, I have an issue. I designed a board with two LTO cells in series connected to the VBAT_SEC. Voltage threshold are set to have 3.3 Undervoltage and 5.35 overvoltage. I connect the cells (now the VBAT_SEC is at 5V, and the behaviour is always the same. I get VBAT?OK only with power from the solar cells. If the sun goes down I have VBAT_SEC disconnected from VSTOR. I tried to short the VSTOR to ground, to attach the battery with the EN pin connected to VBAT_SEC or to ground. No result at all.

Any suggestions?

Shall I put a diode between VSTOR 8system supply) and VBAT_SEC?

  • 0
    TI__Guru**** 166246 points

    Hi Giovanni,

    The internal PFET between VSTOR and VBAT_SEC should turn on to allow current flow from VBAT_SEC to VSTOR until VBAT drops below the internal VBAT_UV threshold of 2.1V.  The only time this will not happen is if you replace the cell at VBAT_SEC while there is a voltage at VSTOR or VBAT_SEC (i.e. the BQ25505 needs to be completely and totally powered down at battery replacement).  VBAT_OK is only for status reporting purposes. /EN only controls the main boost charger switching activity.

    Can you send your schematic? 

    Regards,
    Jeff