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LM8330: Can RESETN be left floating if not needed?

Thomas Bewley
Expert 1030 points
Part Number: LM8330
Other Parts Discussed in Thread: TCA9555, TCA6424A, TCA6507, TCA6418E, TCA8418E

I'm going to be using the LM8330 for controlling a bunch of GPIOs (LEDs, buttons, IC enable and fault pins).  In this setting, I don't think I would ever really use the RESETN pin (correct?).  Can I just leave this pin floating, or should I tie it high?

  • 0
    TI__Mastermind 49040 points

    Hi Thomas,

    In general you should never leave an input pin floating, this includes the NRESET. If the pin were to float to GND, the device would be held in reset and any attempts to communicate with the device or keep its GPIOs set would be lost.

    "I'm going to be using the LM8330 for controlling a bunch of GPIOs (LEDs, buttons, IC enable and fault pins). "

    I just want to make sure you've selected the suitable device for your application here, the LM8330 is quite a difficult device to use. If possible, I would like to steer you towards a device such as TCA9555 or TCA6424A as a alternative for generic GPIO use cases. For LED control, TCA6507 would also be a good fit if you only need to control 7 LEDs.

    Thanks,

    -Bobby

  • 0 in reply to BOBBY
    Expert 1030 points

    Understood on not letting a input pin floating, my mistake.  thanks.

    I'm still exploring the TI catalog for the best device(s) to use.  I need to break out about a bare minimum of 19 GPIOs (a few more would be better), and it needs to have a small footprint - few of TIs other expanders with this many GPIOs are available in packages smaller than 5mm x 5mm, it seems?

    Could you please clarify: is your comment about the difficulty of using this device related to soldering and breaking out its 5x5 0.4mm pitch BGA to the PCB, or more related to interfacing with it to drive GPIOs over I2C?  I've been thinking quite a bit about the former, and I think (with balls soldered directly on top of 8 interior plugged vias, leaving KPY7 as a no connect) my manufacturer should be able to handle placing it - we are also breaking out a 10x10 0.8mm BGA (an MCU) on the same board, the complexity of which seems similar.  

  • 0 in reply to Thomas Bewley
    Expert 1030 points

    PS - From a programming perspective, the (older) TCA6418E looks much simpler to use, and is in the same footprint as a LM8330.  I am leaning now towards implementing a TCA6418E (with a no connect on its center pin) to handle my several GPIO (EN, DRDY, fault, etc) needs, AND a TCA6507 (which, indeed, has some very nice features) for my 7 main LEDs.  Thanks so much for the tip...

  • 0 in reply to Thomas Bewley
    Expert 1030 points

    PPS - Just to follow up: I decided on using a TCA8418E for our GPIOs (plus a TCA6507 for our LEDs).  The TCA8418E, with integrated pull-up resistors, appears to be somewhat better to use as a compact modern GPIO expander than the TCA6418E (with pull-down resistors?), as most modern ICs (sensors, etc) have open-drain interrupt pins (conveniently, more than one of which can be combined onto a single trace), which require a pull UP resistor at the MCU or GPIO expander to which they are connected.  The TCA8418E can handle such modern ICs with its internal pull-up resistors, whereas the TCA6418E requires external pull-up resistors...