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Setting ILIM on the BQ24075 using FT232X charger detection

Michael Allwright
Prodigy 240 points
Other Parts Discussed in Thread: BQ24075

Hi All,

I have a design that I am working on using the BQ24075 and a FT232X USB to UART bridge. The FT232X CBUS pins can be programmed to provide the outputs BCD# and PWREN#. These pins represent whether a USB battery charger is connected and whether it is safe to draw 100mA, 500mA or 1500mA.

These pins are open drain and can be used to effectively control the amount of resistance to ground seen on the ILIM pin, setting the allowable input current to the system.

My question is whether or not ILIM is constantly evaluated, or whether it is only sampled upon start up. Looking at the simplified block diagram on page 8 of the BQ24075 datasheet, it appears that ILIM is fed into an analogue mux which is connected to a comparator. Depending on how simplified this diagram is, I guess ILIM is either constantly evaluated, or at least evaluated every time there is a disturbance on EN1 or EN2...

Any suggestions?

  • 0
    Prodigy 240 points

    From the datasheet we have:

    When VOUT is above VSC, the FET Q1 switches to the current limit threshold set by EN1, EN2 and RILIM and the device enters into the normal operation. During normal operation, the system is powered by the input source (Q1 is regulating), and the device continuously monitors the status of CE, EN1 and EN2 as well as the input voltage conditions.

    I'm now 95% sure my design will work with a variable load on ILIM...

  • 0
    TI__Guru**** 169236 points

    ILIM is constantly evaulted as part of an analog feedback loop.