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BQ25895: designing charger for Lipo battery pack with embedded over-voltage and over-discharge protection

Part Number: BQ25895

Hello, my question of how to do a professional consumer electronics cut off / shut down the overall system before over-discharge kicks in?

Looking at a reference design of by Texas I see protection circuits, charger, and fuel-gauge but I am still thinking how the product will shut off itself properly?

For instance, on my system, I would probably not want the battery to drop below 3.2v as my system is using 5V domain which is OTG boost supplied by BQ25895 which based on the datasheet battery voltage falling below 3V will cut off 5v boost voltage. The problem I see here is that my 5V domain will shut off earlier than my SYS out voltage so that means there might be some part of the system are not working while low voltage things like my MCU will be running fine till further discharge. The problem I would want to solve is to sync the cut-off, 5V(OTG) collapse and the entire system to shut off till charger is present ? how to achieve this efficiently?

One idea I have in mind is to add the comparator and p-channel FET source directly to SYS output and setting the threshold voltage at 3.2V to cut off SYS output, likely to tie the reference voltage from the battery directly with a divider but I am open to much more efficient idea if there's

  • Hi,

    Referring to Supplement Mode on the d/s, BATFET turns off to exit Supplement Mode when the battery is below battery depletion threshold (2.15V-2.5V).

    Referring to 8.2.5 Boost Mode Operation from Battery on the d/s, The boost output is maintained when BAT is above VOTG_BAT threshold. The device exists boost mode when the battery drops below 2.6V-2.9V.

    The device registers provide the device status, ADC monitoring information on VSYS, VBAT etc. The host may turn off Q4(BATFET) via REG09[5] to disconnect the battery when needed.



  • Ning, thanks for the explanation, just got to know I can switch the state of Q4. 

    Do you think this would work, where I periodically monitor the VBAT and when it's below my threshold value, host switch off the Q4, and when charging applied, should I manually turn on Q4 back?

  • Hi,

    Q4 needs to be enabled when charging.