• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Answers 1 answer
  • Subscribers 34 subscribers
  • Views 1305 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

PCA9539: Reset Function

David Schanin
Intellectual 270 points
Part Number: PCA9539
Other Parts Discussed in Thread: TCA9539

Seems that all of the I2C I/O expander parts have these tight power supply power-up requirements which if violated will cause the part to lock up, per the description.  I am using this part in an application where such a power-on lockup would be intolerable.  The PCA9539 has a -RESET pin but I can't find a specific description that would convince me that this pin will reset such a power-on locked up part.  Does anyone have any information or experience with this issue?  Thanks very much.

  • 0
    TI__Genius 16450 points

    Hello David,

    I would actually recommend looking at the TCA9539. It is exactly the same software wise, P2P (if it has the same package that you are using in the PCA part), and has a revised and improved power on reset circuit that can handle ramp rates from 0.1 ms to 2 seconds without latchup issues. The TCA part is also the same price or less. It is a newer part that also supports a wider VCC voltage range (down to 1.65V instead of 2.3 V)

    However, if you are unable to upgrade to the newer part, you may ramp outside of the power supply requirements, if you ensure that you toggle the reset pin after the power supply is fully ramped. The reset pin will reset the state machine to default values, recovering from a lock up condition.

  • 0 in reply to Jonathan Valdez
    Intellectual 270 points

    Thanks Jonathan.  I will use the TCA part.  As long as I am guaranteed that I can recover the chip to operational status by asserting the -RESET line, then I am OK.  Maybe I missed something in the TCA spec about the 2 seconds so I will dig further.  Thanks again.

  • 0 in reply to David Schanin
    TI__Genius 16450 points
    Ah my mistake. On the TCA9539, there is no upper limit. I was thinking of another TCA part. Note that I refer to the TCA prefix instead of PCA.

    On the TCA parts, I have not been able to get the part to latch up with power sequencing testing, but due to the design of the reset pin, if it ever did happen, a toggle of the reset pin forces all internal state machines to defaults.

    As a bit of background, in the PCA devices have a power on reset circuit that is responsible for resetting the internal state machines to defaults. In certain ramp conditions, the POR circuit was not triggered, and the device would be in a random state. This is the latch up condition. When the reset pin is toggled, it forces that POR circuit to activate (provided that the power supply is ramped), resetting all state machines.

    With the more advanced simulation technologies available to us, when we designed the newer TCA family of products, we were able to make a much more robust circuit capable of responding to both fast and very slow power supply ramp rates.
  • 0 in reply to Jonathan Valdez
    Intellectual 270 points
    Thanks very much Jonathan. I will use the TCA part and have the micro toggle the -RESET pin as part of its startup, or if it ever hangs.