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BQ24725A: why resistors connected to SRP and SRN are different value?

Howard Zou
Genius 12365 points
Part Number: BQ24725A

Hi,

1. In datasheet figure 18, why the recommended resistor connected to SRP is 10ohm, SRN is 7.5ohm? In datasheet it says it's to limit the reverse current, but can we make them the same value?

2. The recommended value is for pre-charge current >192mA, but now my customer would like to set pre-charge current to 100mA, what modification should we do?

  • 0
    TI__Guru**** 165886 points
    Howard,

    Regarding 1, the resistor difference is to control the phase delay between the two signals. With the voltages at SRN and SRP in phase, the current measurement is more accurate.

    Regarding 2, the BQ24725A does not automatically lower the charge current to precharge for lower battery voltages. The host is responsible for writing the charge current to the desired precharge current level. The lowest charge current level is 128mA with a 10mohm sense resistor. To go to lower current, you would need to increase the SNS above 10mohm.