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BQ24297: Operation without battery is unstable

Art Mecina
Genius 16655 points
Part Number: BQ24297

Hi 

One of our customer is using BQ24297RGER in their application.

Their part is working as expected with a battery installed. However, in some cases, their system will need to operate without a battery. (Power will be supplied via USB 2A charger.) In this scenario, the BQ24297 will output the voltage set by the I2C register (3.8V),

But after some time, The load changes such that it is trying to draw more power than the ILIM is set for.
Does this trigger INT when the system is running off the USB charger? If so, when does it fire in relation to shutting down?

Appreciate your support on this.

Regards,

Art

  • 0
    TI__Guru 57541 points

    Hi,

    Yes, the device may operate normally without a battery.

    Thanks,

    Ning.

  • 0 in reply to Ning T
    TI__Genius 16655 points

    Hi Ning,

    Thanks for the information.

    However i just like to clarify the concern of the customer.

    The scenario he is asking about is like this:

    The device is powered and operating properly.
    The load changes such that it is trying to draw more power than the ILIM is set for.
    Does this trigger INT when the system is running off the USB charger? If so, when does it fire in relation to shutting down?


    Best regards,

    Art

  • 0 in reply to Art Mecina
    TI__Genius 16655 points

    Hi Ning,


    Good day.

    I just like to update with regards to this inquiry.

    Best regards,

    Art

  • 0 in reply to Art Mecina
    TI__Genius 16655 points

    Hi Ning,

    Good day.,

    Any news with regards to this inquiry?

    Thanks and regards,

    Art

  • 0 in reply to Art Mecina
    TI__Genius 16655 points

    Hi Ning,

    Good day.

    To better understand customer inquiry, I referred him to this post so that he can explain his query further
    and get back to you immediately in case you have some clarifications.

    Regards,

    Art 

  • 0 in reply to Art Mecina
    TI__Guru 57541 points

    Art,

    ILIM pin sets the maximum input current limit by regulating the ILIM voltage at 1V. A resistor is connected from ILIM pin to ground to set the maximum limit as IINMAX = (1V/RILIM) × KILIM. The actual input current limit is the lower one set by ILIM and by I2C REG00[2:0]. The minimum input current programmed on ILIM pin is 500 mA.

    To meet maximum current limit in USB spec and avoid over loading the adapter, the device features Dynamic Power Management (DPM), which continuously monitors the input current and input voltage. When input source is over-loaded, either the current exceeds the input current limit (REG00[2:0]) or the voltage falls below the input voltage limit (REG00[6:3]), the device may enter DPM. During DPM mode (either VINDPM or IINDPM), the status register REG08[3] will go high.

    The following events will generate a 256-µs INT pulse:

    1. USB/adapter source identified (through PSEL or DPDM detection, and OTG pin)

    2. Good input source detected – not in sleep – VBUS below VACOV 

    3. Input removed or VBUS above VACOV threshold

    4. Charge Complete

    5. Any FAULT event in REG09 For the first four events, INT pulse is always generated. For the last event, when a fault occurs, the charger device sends out INT and latches the fault state in REG09 until the host reads the fault register.

    Thanks,

    Ning.

  • 0 in reply to Ning T
    Prodigy 70 points

    Ning

    Thanks for the reply.  We understand that principle.  

    The question arises: When does INT fire in relation to the chip shutting down due to overcurrent?

    ie. Can our micro monitor the INT pin using an ISR and turn off the load in time to keep the BQ24297 from shutting down?

    Thanks,

    Chris

  • 0 in reply to Chris Lange
    TI__Guru 57541 points

    Chris,

    Referring to the info below, when REG08[1] goes high, the host may take proactive measure.

    9.3.5.2 Thermal Regulation and Thermal Shutdown

    During charge operation, the device monitors the internal junction temperature TJ to avoid overheat the chip and limits the IC surface temperature. When the internal junction temperature exceeds the preset limit (REG06[1:0]), the device lowers down the charge current. During thermal regulation, the status register REG08[1] goes high. Additionally, the device has thermal shutdown to turn off the converter. The fault register REG09[5:4] is 10 and an INT is asserted to the host.

    Thanks,

    Ning.