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BQ25173: Schematic review & Question

CHO SR
Genius 3415 points
Part Number: BQ25173


Hi,

Customer wants to recharge the supercapacitor by applying BQ25173.

Please review the schematic.

FAST CHARGE CURRENT 0.3A / VREF 3.52V

Add, customer's question.

Q1 : VUSB not connected (IN = Floating), SUPERCAPAICTOR (Out = 3.6V) conditions

/CE pin Low - Quiescent current? /CE pin High - Quiescent current?

Q2 : Why is there a current difference between connecting the bottom resistor of FB with GND and connecting it with /PG, and what is the current difference?

Q3 : For /PG and STAT, I would like to get the following input from the HOST with pull-up. Is it possible?

- /PG : USB Detect

- STAT: Charging, charging complete. 

  • +1
    TI__Mastermind 20570 points

    Hi Cho,

    Regarding 1, /CE function is not active when no input is connected. It should be the same as specified in the EC table IQ_OUT.

    Regarding 2, /PG is a open drain output. You can refer to the function block diagram on datasheet page 11, it is connect to ground with NMOS. If the feedback resistor divider connects to GND, then the leakage through these two resistor will always be there (I = V/R). If it connect to /PG, when VIN is floating, the NMOS connects PG to GND is off.  Thus, the leakage current will be lower.

    Regarding 3, what kind of USB Detect are your referring to? If you are only want to detect if a valid input source is plugged in, then yes. /PG will only be pulled low when a valid input source is plugged in.

    You can refer to table 7-1 on page 13 for charge status operation. On BQ25173 when VFB<98% of VFB_REF, STAT pin is high. When VFB>98% of VFB_REF, STAT pin is low.