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BQ21040: input and output requirements

BIT_RF
Prodigy 150 points
Part Number: BQ21040
Other Parts Discussed in Thread: BQ24230, BQ24073

Hello.

I have the design in figure. I need to know if the BQ21040 is working well when VUSB and EXT_VIN are not present. I mean:

the Vout of BQ21040 is VBAT and its Vin is VBAT - Vf of D19. Is this correct? VBAT is a li-ion battery.

Thanks and best regardsbq21040_sch.pdf

  • 0
    TI__Guru* 75656 points

    Hello

    USB / Adapter connected is probably OK. Diode OR will keep the battery out of circuit and voltage at input to charger should be high enough to charge battery.

    NO USB / Adapter applied needs more study. Battery will be connected to charge input thru diode. But the input voltage to charger is diode drop below battery (Vin < Battery), will not charge battery, internal blocking diodes will prevent current flow.  BUT voltage is above UVLO and unit is on and quiescent current may be an issue.

    How large is battery? Can you tolerate large quiescent current?

     

    Also note that the BQ24230 is a power path device that will manage battery charging and current to system load in a more efficient manner, it may be a better option.

  • 0 in reply to Bill Johns
    Prodigy 150 points

    Hi Bill.

    Thanks for your reply!

    Attached a new design with BQ24073.

    Is it correct? When there is no Charger in, is it correct to assume the Vbat on the out pin?

    Thanks.

    Bruno B.BQ24073_sch.pdf

  • 0 in reply to BIT_RF
    TI__Guru* 75656 points

    Hey Bruno

    This look pretty good.

    A couple of things to tweak.

    1.) The TMR resistor should be 46K for 6 hr

    2.) OUT should have a 4.7uF capacitor for stability.

  • 0 in reply to Bill Johns
    Prodigy 150 points

    Ok.

    Thanks you again