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BQ2403x family - Disabling all supplies?

Bob Miller76124
Prodigy 30 points
Other Parts Discussed in Thread: BQ24035, TMP300

 

I have a few questions/comments on the BQ24035 part that I plan to use. I assume it applies to the entire family.

1) I have mobile computer design where I would like to have a temperature monitoring chip (TI TMP300) to shut down all power to the system with a temperature fault - in my case either AC Adapter, USB or Battery. The over temperature may be due to high ambient temperature or failure of a component that causes overheating. Because of the possibilitiy of component failure (our downstream power supply chip, for example) I can't depend on the processor to decide to shut the system down, instead I need a HW over-ride. Your CE signal input looks close, however still allows the battery to supply power to the system.

 - Is there anyway (tricks?) to shut off all power (AC, USB and BAT) to OUT without significant external components?

2) As a future design suggestion:

 - It would be very nice to have the battery charge termination point be pin selectable between 4.1 and 4.2V. 4.2V tends to be more industry standard providing additional capacity, but with 4.1V providing significantly increased battery life. Some of my customers would prefer the latter as a tradeoff.

 - CE- why is it setup as active high enable? Unless I am doing something wrong it seems much simpler to be active low. Active High makes the circuit design much more complicated because of the input voltage domains (up to 18V) and CE is limited to 7V max. And you have to develop your own high voltage from the AC/USB voltages to provide the active high signal since I can't depend on any supply being present (even the battery).

Thanks for your help,

Bob

 

 

  • 0
    TI__Mastermind 45250 points

    Bob,

    You are correct in that the BQ24035 will not "totally" shut down when the CE pin disables the chip. It was designed to intelligently manage the power sources that are available so that there would always be at least one source of power available to the system. In this case, with no power to drive the CE pin (0V) from external sources, there would still be a power available to the system if it was needed.

    The only options to stop the BQ24035 from supplying battery power to parts that are still operating downstream in the situation described above would be to use external components (as you suggested) or to use the TMP300 (or a similar device) to also shut down any of the parts that are drawing power from the BQ24035.

    This part was originally released in 2004 and the designers specifications at that time called for logic level control signals. These specifications are normally derived due to feedback and suggestions from external customers. I do not know why they chose active high, but I am sure that in future designs they will consider your concerns when specifying new parts.

    Please let me know if you have any further questions.

    Richard Elmquist