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BQ25895: Query on current available on sys pin

Shreenidhi Patil
Expert 3976 points
Part Number: BQ25895

My customer has following query on BQ25895 .

 

  1.  Can I draw power from SYS and PMID pin simultaneously. If yes how much
  1. How much current can be drawn from Sys pin when , when Vbus is present , and No load on PMID

  1. what voltage will appear on SYS pin,  if Battery is not connected at all in the system  and external power is connected to Vbus 

  • 0
    TI__Guru**** 167066 points

    Shreenidhi,

    Regarding 1, V(PMID) =V(VBUS) - IBUS*RDSonQ1. There is no current limit protection out of PMID if you pull current from PMID through the Q1 FET between VBUS and PMID. PMID is the input to the buck converter that provides SYS. Any current that you pull from PMID will not be available to the SYS output. Using efficiency power balance, eff=VSYS*ISYS/(VBUS*(IBUS-IPMID)), where IBUSmax=3.25A, VBUSmax=13.5V and eff is estimated from datashseet efficiency curves, you can predict ISYS.

    Regarding 2, see 1 above.

    Regarding 3, with no battery connected and charge disabled, V(SYS) = VSYSMIN+150mV. VSYSMIN=3.65V.

  • 0 in reply to Jeff F
    Prodigy 200 points

    Hi Jeff,

    when adapter is connected to VBUS and i want to set input current as 2.4A, I have to set  VD+/VD- within V2P7_VTH . If my input is 12v on vbus, can use a resistor divider of 11.3k and 3.24k (2.67V)and connect to D+ and D- pin. will this put the IC BQ25895 in non standard adapter divider 4 option to set current limit to 2.4A

  • 0 in reply to Ajay Kumar55
    TI__Guru**** 167066 points

    Ajay,

    I think it will be easier to simply short D+/D- pins together, which sets the internal IINDPM register to 3.25A and using the ILIM resistor to clamp IINDPM to 2.4A.  Using D+/D- to set input current is only intended to be used until the host is available to enumerate USB and then change the IINDPM register.