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BQ25798: PMID maximum current in OTG regulation

Juan Aparicio Jimenez
Intellectual 2200 points
Part Number: BQ25798
Other Parts Discussed in Thread: BQ25730, BQ25720

Dear e2e experts, 

My customer asked for the  PMID output of the BQ25798 – How much current can flow ? 

The customer needs to regulate the backup at 12V with 41.5W, which leads to 3.46A in the OTG mode. 

I see the IOTG_RANGE is:

 

Is there somehow we can achieve the 12V 3.46A in the OTG regulation from the battery?

Thanks and best regards,

Juan.

  • 0
    TI__Guru**** 171596 points

    Hi Juan,

    The IOTG_RANGE you show above is if the output is from VBUS and IOTG (IINDPM) current limit is active.  There is no current limit circuit on the PMID so its output current is only limited by efficiency [41.5W / (VBATmin*IBATmax)] and the charger's cycle-by-cycle current limit.  What is the lowest battery voltage and max battery discharge current allowed?

    Regards,

    Jeff

  • 0 in reply to Jeff F
    TI__Intellectual 2200 points

    Hi Jeff,

    Thanks a lot for your answer!

    So there's the limit on the IOTG when outputing to the bus through VBUS, but this is not the case when OTG is used in backup mode, right?

    Another question: could you explain further the backup mode through VBUS?

    n this case the PMID rail is powered by the adapter through VBUS and it is limited 3.3A? as per DS IVBUS Input current < 3.3 A

    Thanks and BR,

    Juan. 

  • 0 in reply to Juan Aparicio Jimenez
    TI__Guru**** 171596 points

    HI Juan,

    Yes, there is an 3.3A current limit circuit when IOTG comes out of VBUS but not PMID.  However, that circuit can be disabled.  We do not recommend for normal use as we don't have much data on that type of operation.   

    Regards,

    Jeff

  • 0 in reply to Jeff F
    TI__Intellectual 2200 points

    Hi Jeff,

    Thanks a lot! 

    Can the 3.3A current limit be disabled when PMID is outputting from VBUS? Just as in the second backup mode: 

    Thanks and best regards, 

    Juan.

  • 0 in reply to Juan Aparicio Jimenez
    TI__Guru**** 171596 points

    Juan,

    There is no current limit from VBUS to PMID. The resistor (really a FET) between VBUS and PMID is used to measure the input current and then feed that information to the PWM modulator.  Once the input current reaches the threshold, the PWM modulator clamps the converter duty cycle which limits the converter output current.  You can disable this feature using REG0x14b2.  This bit also disables the reverse mode/OTG current limit.  We have very little data on currents higher than 3.3A from VBUS to PMID or output of PMID in reverse mode/OTG mode.  Other protection features like cycle-by-cycle current limit or thermal regulation will likely kick in and limit output power.  I recommend that your customer move to a controller with external FETs like the BQ25720 or BQ25730 families.

    Regards,

    Jeff