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BQ25890: ILIM pin for BQ25890

Zhang Excellent
Prodigy 140 points
Part Number: BQ25890

Tool/software:

As we know, for BQ25890,IINLIM or  IDPM_LIM can be used by DPM. But what's the usage of ILIM pin controlled input current limit? That's to say if the input current limit of Charger is determined by ILIM pin, what will happen when the actual input current is over this input current limit  determined by ILIM pin, compared with DPM function?

  • 0
    TI__Mastermind 31720 points

    Hello, 

    Thank you for reaching out via E2E. 

    The actual input current limit of the BQ25890 will be the lower value between the register setting in REG00 and resistor based setting at ILIM pin. 

    Zhang Excellent said:
    That's to say if the input current limit of Charger is determined by ILIM pin, what will happen when the actual input current is over this input current limit  determined by ILIM pin, compared with DPM function?

    This scenario will not occur because the BQ25890 will not attempt to draw more current than the input current limit determined by ILIM pin. 

    Best Regards,

    Garrett

  • 0 in reply to Garrett Kreger
    Prodigy 140 points

    How much current will be drawn from input source depends on the system load.So if the system load is heavy enough to draw input current more than the limit determined by ILIM pin，what will happen？

    Or why and how can the charger prevent the input current from exceeding the limit set by ILIM pin？

  • 0 in reply to Zhang Excellent
    TI__Mastermind 31720 points

    Hi Zhang, 

    Even if system load increases BQ25890 will not attempt to draw more current from input adapter than input current limit. The device is able to measure the input current before the buck converter and internal control prevent current draw from exceeding the limit set by ILIM pin/register setting. 

    Zhang Excellent said:
    So if the system load is heavy enough to draw input current more than the limit determined by ILIM pin，what will happen？

    First the BQ25890 IC will enter dynamic power management where charge current is reduced so that majority/all of input current can support SYS load. figure 9-3 in the datasheet helps to illustrate this. 

    If SYS load is still larger than input adapter can support with charge current reduced to 0A then device will enter supplement mode where battery discharges to help support SYS load. 

    Best Regards,

    Garrett

  • 0 in reply to Garrett Kreger
    Prodigy 140 points

    I have always been understanding this in that ILIM hardware pin determined actual input current limit value is not applicable（or cannot lead to） to DPM or Supplement Mode. Because in my mind，only IinDPM register by I2C/SMBUS determined limit value can activate DPM or DPPM（supplement mode）and ILIM hardware pin determined actual input current limit （EN_ILIM=1）cannot lead to DPM or DPPM even if IinDPM register value is larger than ILIM pin set value which results in the actual input current limit deriving the lower one—value set by ILIM hardware pin. So I‘m somewhat wrong about ILIM pin regarding DPM and DPPM.

    Another question，Is there any register to restore the value of ILIM hardware pin limit value or is there any register to restore the voltage on ILIM pin in real time？

  • +1 in reply to Zhang Excellent
    TI__Mastermind 31720 points

    Hi Zhang, 

    How the BQ25890 responds to the input current limit is the same no matter if it is set by register or ILIM pin. They are simply 2 methods to set the input current limit and the actual input current limit used by the device will be the lower of the 2. The hardware pin input current limit value is applicable to the device entering DPM and supplement mode. 

    Zhang Excellent said:
    Is there any register to restore the value of ILIM hardware pin limit value or is there any register to restore the voltage on ILIM pin in real time？

    No, the ILIM hardware pin limit value is not stored in registers. For example, if hardware pin limit is 500mA and register setting is 1A the device will adhere to 500mA limit, but neither REG00 or REG13 will report input current limit as 500mA. REG13 bit 6 will indicate if the device is in IINDPM status (i.e. input current has reached limit value) no matter if register set limit or hardware pin limit is used. 

    Best Regards,

    Garrett

  • 0 in reply to Garrett Kreger
    Prodigy 140 points

    Is there any register or method to disable IinDPM or VinDPM for BQ25890？ How about other IT chargers with these two features？If not，is this means that both IinDPM and VInDPM are compulsory for a charger if it has such features？

  • 0 in reply to Zhang Excellent
    TI__Mastermind 31720 points

    Hi Zhang, 

    There is no register or method to fully disable IINDPM or VINDPM feature. In general all our chargers have some form of input protection. Some lower cost linear chargers only have VINDPM rather than both IINDPM and VINDPM. 

    Zhang Excellent said:
    If not，is this means that both IinDPM and VInDPM are compulsory for a charger if it has such features？

    These features are not required for a charger, but the general customer does use the features to prevent overloading their input adapter. 

    If you wish to disable VINDPM and IINDPM the best option is to set VINDPM and INDPM thresholds "out of the way". That would mean setting VINDPM to minimum threshold of 3.9V and INDPM to maximum threshold of 3.25A. 

    Best Regards,

    Garrett

  • 0 in reply to Garrett Kreger
    Prodigy 140 points

    Ok，setting a out-of-scope value for IinDPM and VinDPM can be identical to disabling IinDPM or VinDPM.

    In the notebook market there is always a charger for charging a battery， but no battery exists in mini PC，however DCIN adapter is still used for powering a mini PC（NUC），is there any acheme similar to IinDPM or VinDPM to prevent adapter from overload in TI power manage solutions？

    Of course，TI charger IC can work in mini mini PC without battery to protect the adapter，but it’s much more expensive without many features fully employed.

  • 0 in reply to Zhang Excellent
    TI__Mastermind 31720 points

    Hi Zhang, 

    Zhang Excellent said:
    setting a out-of-scope value for IinDPM and VinDPM can be identical to disabling IinDPM or VinDPM.

    It is not identical to not having the features at all, but setting thresholds to min and max values respectively will minimize the chance of BQ25890 operating in IINDPM or VINDPM condition. 

    Zhang Excellent said:
    is there any acheme similar to IinDPM or VinDPM to prevent adapter from overload in TI power manage solutions？

    If you are considering selection of a standard DC/DC buck converter rather than a battery charger specific buck converter I recommend you make a new E2E post so appropriate expert can recommend the proper part and answer any additional questions. 

    I can continue to help answer any questions pertaining to battery charger ICs such as BQ25890 in this thread. 

    Best Regards,

    Garrett