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Original question:

BQ24157: A question about system load connected position

BQ24157: A question about system load connected position

Shawn Morrison
Prodigy 35 points
Part Number: BQ24157
Other Parts Discussed in Thread: BQ25611D

Hi,

I have the same question as

https://e2e.ti.com/support/power-management/f/196/t/636936#pi320995filter=all&pi320995scroll=false

and it was not properly answered. I agree the battery must stay connected to CSOUT but the question is can a system load be connected to CSIN? This is of course providing that the maximum battery charge current plus the maximum system load does not exceed the external power input source or the dc-dc cycle by cycle current limit. Are there any other concerns?

  • 0
    TI__Guru**** 167196 points

    Hi Shawn,

    I do not recommend connecting a system load to CSIN because 1) the CC loop is effectively disabled because not all output current is flowing through the sense resistor and 2) the output capacitor is on the other side of the SNS resistor, which will create large ripple and transient drooping.   In theory, you could add additional capacitance at CSIN and mitigate 2.   For 1, in theory, the CV loop should prevent overvoltage and the input current loop or input voltage limit loop (and as last resort cycle by cycle current limit) will prevent output over voltage and/or limit the input current.  We haven't tested either theoretical modifications.  I still recommend moving to an newer device with power path, like BQ25611D or similar.

    That said, I have seen customers split the current sense resistor into 2 series resistors, tap off the middle for SYS, with added capacitor and then connect the battery at the end of the other resistor.  This also is not a fully tested configuration.

    Regards,

    Jeff