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BQ25790: design check

Kai Lai
Expert 5796 points
Part Number: BQ25790

Hi Team,

My customer would like to use our BQ25790.

They expect it will charge a 3S battery when the Vin is 15V and 20V(PD source).

But when the VBUS is 5V /9V they don't expect charger work.

Can we set the reg 0x5 input voltage limit as 15V and it can stop charger work to charge and do not provide power to Vsys when the VBUS is 5V/9V?

Thanks.

Kai

  • 0
    TI__Guru*** 143880 points

    Hi Kai,

    The VBUS OVP is 7V default.  That needs to be increased.  VINDPM threshold autosets to either 0.7V or 1.4V less than the input voltage sensed at initial power up.  If the charger is powered up first by a high voltage and then that input voltage is lowered, the VINDPM threshold does not automatically lower.  So, the host must write to the VINDPM register to lower the VINDPM threshold below the applied voltage at VBUS.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    TI__Expert 5796 points

    Hi Jeff,

    Thanks for your reply.

    1. So if I set VINDPM threshold at 14V(if I expect that a 15Vin from PD adaptor) then if at this moment the VBus voltage is 5V/9V, then charger will disable charge function? 
    2. Since it will use a the PD adaptor as the input power, the voltage will always start from 5V then raise to 15 or 20V, so host will need to set the  VINDPM threshold to 14V or 19V based on the PD level raise to. But before host write 14 or 19 to VINDPM threshold registrar, since  there is a 5V at Vbus, will charger enable the charger at this moment ?
    3. If question2 will charge, So it looks like an NVDC didn't fit for this application right ?
      Unless customer can control the adaptor source, if it is not 15V/20V, then do not pass to the Vbus of charger.
    4. Does we have a Hybrid boost charger with I2C controlled, integrated switch MOSFET and 3A charge current ability solution can use here ?

    Thanks!

  • 0 in reply to Kai Lai
    TI__Guru*** 143880 points

    Hi Kai,

    Regarding 1, if VINDPM =14V and VBUS<14V, the charger reduces input current to zero because it thinks the adapter has crashed.  This effectively sets IOUT=ISYS+ICHRG = 0A.

    Regarding 2, yes.

    Regarding 3, the BQ25790 is a NVDC buck-boost charger so the buck-boost converter provides the higher of the MINSYS or battery voltage to SYS regardless of the input voltage being higher or lower than the MINSYS or battery voltage.  A traditional (non-NVDC) charger passes its input to SYS. Battery charging can be disabled using the CE pin or I2C register bit.

    Regarding 4, the BQ25790 is the only TI integrated FET charger for up to 20V input.

    Regards,
    Jeff