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BQ24172: Battery/system sense resistor

Scott Mullin
Prodigy 20 points
Part Number: BQ24172
Other Parts Discussed in Thread: BQ24170

Hello,

The system examples in the datasheet for the BQ2417x, in figure 23 the system voltage is taken prior to the sense resistor Rsr, and in all of the other figures the system voltage is taken after the sense resistor Rsr.  Which is correct?  Is figure 23 only applicable to BQ24170?  What affect will this have on the BQ24172?

Thank you 

Scott Mullin

  • 0
    TI__Mastermind 25800 points

    Hey Scott,

    There are three figures in the application section. All three are correct, and it really depends on the configuration you desire.

    Figure 23 has no external BATFET and the system rail is connected before the RSR resistor. Here, the system can pull current independent of the charge current. The charger will attempt to regulate the differential voltage across SRP/SRN to give the ISET charge current to the battery. All the while, the system rail can pull current without tapping into this regulated current. Or until 

    On other hand, Figure 25 shows a scenario where the system rail and the battery share the ISET charge current, because the system is after the RSR resistor.

    Figure 24 added a power path using an external BATFET.

    Regards,

    Joel H