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BQ25570: Pin Connect question of BQ25570

Jimmy Lai
Expert 6845 points
Part Number: BQ25570

Dear team,

1. If customer only need to connect to either battery or system load.

Can VBAT and VOUT be connected to only one of them? Or both should be connected? 

2. If the customer wants to increase the capacitor in Vstore to charge VBAT, will it have any impact ?

3. What does the definition of OK_PROG  mean?

Many Thanks,

Jimmy

  • 0
    TI__Guru*** 143880 points

    HI Jimmy,

    Regarding 1, VBAT is connected to VSTOR through the internal PFET which provides undervoltage (overdischarge) protection.  VSTOR is the output of a boost converter.  VSTOR is also the input to the buck converter that provides VOUT.  I do not recommend connecting VBAT=VOUT because that shorts out the buck converter.   The buck converter operates in 100% mode, connecting VSTOR=VBAT to VOUT, if VSTOR=VBAT < VOUT set point, which essentially does what you want.

    Regarding 2, the capacitor on VSTOR can be larger but it will increase cold start charge time if used.

    Regarding 3, VBAT_OK pin is the output of an independent comparator with thresholds set at VBAT_OK_PROG and VBAT_OK_HYST.  The intent is to connect the VBAT_OK output to the system enable line so that the system is only running when the battery has risen above the VBAT_OK_HYST threshold.  If the battery falls below the VBAT_OK_PROG threshold, VBAT_OK signal goes low which signals the system to turn off.  

    Regards,
    Jeff