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BQ24253: Behavior of V_sys and I_sys (BQ24253RGER)

Gordon Liu
Intellectual 855 points
Part Number: BQ24253

Dear Sir,

I use the chip to charge the Battery but I'm confusing 2 parameter; V_sys and I_sys.

1: If Vdpm set= 4.5V, Vin=4.7V, what is the V_sys??

2: If Ilim=1A ,Iset= 0.5A and I_bat=0.5A(Changing), what is the I_sys??

  • 0
    TI__Guru**** 166106 points

    Hi Gordon,

    Regarding 1, V(SYS)=max of MINSYS or VBAT+~50mV unless input power (VIN*IIN)*efficiency is too low to supply VSYS*(ISYS+ICHG) then the charger goes into supplmement mode and VSYS=VBAT-RDSon*ISYSsupplement.  

    Regarding 2, the system load pulls ISYS.  The charger prioritizes system load over charge current.  Maximum output power (VSYS*(ICHG+ISYS)) will be limited by input power =VIN*IIN*efficiency.  Assuming you VIN=5V and ILIM=1A, the charger has 5W*efficiency of output power to send to ISYS+ICHRG.  ISYS takes priority.  Datasheet efficiency curves can help you estimate efficiency for a given VSYS voltage.

    Regards,

    Jeff 

  • 0 in reply to Jeff F
    Intellectual 855 points

    Hi Jeff,

    Thanks for your responses quickly.

    1: About Vsys,  It's variable from 3.5V~4.2V base on the Vbat (Datasheet/ figure 15) does it right??

    2: If the Battery energy is full and disconnect the Vin_5v connector, what is the transition time of Vin => Vbattery?? 

  • 0 in reply to Gordon Liu
    TI__Guru**** 166106 points

    Hi Gordon,

    Regarding 1, yes.  SYS follows the battery up as it charges.

    Regarding 2, the transition time from input power attached to HiZ/sleep mode is in the 10's of us range.  

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Intellectual 855 points

    Hi Jeff,

    My english is poor.

    "It is in the 10's of us range"; does it 10us ~ 19uS ??

  • 0 in reply to Gordon Liu
    TI__Guru**** 166106 points

    Hi Gordon,

    yes, I should have been more clear, 1-20us.

    Regards,

    Jeff