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BQ25504: system can't be activated with depleted battery

K.Yaita
Guru 29720 points
Part Number: BQ25504

Hi Team,

My customer is evaluating bq25504EVM.
I heard system that loads VSTOR can't be activated (power on) forever with depleted battery.
It seems the system requires big input power at power on itself but energy source (input of bq25504) outputs smaller.

I believe it is possible case, but may I have your comments?

Best Regards,
Yaita / Japan disty 

  • 0
    Prodigy 20 points

    Hi there! 

    Have you got your answer? 

    I have been trying to design a simple solar application using this BQ25504 chip. I have ran into some problem here. when I connect a full battery about 3.7 v to the VBAT, I am expecting the PFET inside the chip turn on and short VSTOR to the VBAT feed the load (a MCU). but this does not happen and the PFET does not switch on. is this how the system work? or am wrong somewhere. 

    if I apply a 470 mV voltage from an external source (could be solar / power supply), the system start ruunig the boost and connects the battery to the VSTOR, it stays connect even if I remove the external source which is good.  

    do you have any suggestion on this please. 

    kind regards,

    Roosbeh

  • 0 in reply to Roosbeh Almasi
    TI__Intellectual 2050 points
    Apologies for being so late to this post.

    K. Yaita,

    The system load on VSTOR will be supplied by the input until the input is no longer sufficient enough. The battery will then help supply the load. The battery can supply power to the load up until the the voltage drops below the VBAT_UV threshold. At that point, the internal PFET is turned off. This feature keeps the battery from being discharged too much. The threshold is set externally with resistors.

    Roosbeh,

    There needs to be voltage on the input to initially activate the internal control circuitry to turn on the PFET. Plugging in VBAT alone won't turn on the PFET. Once connected, the input can be disconnected and the battery will supply the load on VSTOR until VSTOR drops below the VBAT_UV threshold.

    It sounds like this is what you have been seeing and is the expected functionality of the device.

    -Joe