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BQ25570: Battery Drain Fast

Part Number: BQ25570
Other Parts Discussed in Thread: SM74611

HI ,

I am using BQ25570 and below is the configuration?

1. Solar Panel (5V, 2.6W) to BQ25570

2.a) BQ25570 to 4 Cell parallel x 18650 Battery

    b) BQ25570 to SM74611 to Load. 

The problem I’m found is the battery voltage drops very quickly (voltage value ~ 0-1V) and the resistance from VBAT pin to GND is ~ 40 Ohm. 2/4 devices encountering this case is in storage state (not yet put into actual operation), so Solar charger feature not yet active.

- The power of Solar Panel is larger than the input power allowed of BQ25570, but 2/4 devices are in storage state and I had a small test is using Solar Panels 9V & 12V for the input of BQ25570, the result is BQ25570 still works normally 

- Quality of Battery is not good ( internal resistance of Battery is of large value) so it affecting to IC operation

- Activity characteristic of the Diode cause this case 

Possible to give some advise, if you need schematic, that i can share to you. 

 

  • Hi XJ,

    If you remove the 2 of 4 devices measuring 40 ohms from BAT to GND from the IC, and measure only the IC pins, not the board, does the IC still measure 40 ohms from BAT to GND?  When attaching the battery to BAT and GND, if both VSTOR and BAT are below 100mV and V(BAT)>2.2V, then the PFET between BAT and VSTOR turns on.  The IC itself is powered from VSTOR.  The battery will then power the IC and any load at VSTOR.

    The BQ25570 input is not rated for higher than 5.5V on the input, will likely be damaged if you apply a higher voltage and therefore we cannot warranty this operation.

    Regards,

    Jeff

  • HI Jeff,

    Resistance from VBAT pin to GND still ~40 Ohm when we measured only the IC pins. The voltage on VSTOR = VBAT = 4.1V in the board works normally.

  • XJ,

    If the IC was unsoldered from the PCB and the resistance from the IC's VBAT pin to GND is still 40 ohm, then the IC is damaged.  The only other explanation is if VIN_DC > VBAT_OV threshold, then the charger turns on the pull down FET on VIN_DC which attempts to pull down the input voltage so that it will not overcharge the battery.  If the PFET is on there is a path through the inductor to VSTOR and VBAT.

    Regards,

    Jeff