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SX Latch-Up — Parallax Forums

SX Latch-Up

william chanwilliam chan Posts: 1,326
edited 2008-02-05 19:49 in General Discussion
I wonder if anybody has seen this before.
This latch-up problem is always there since many years ago.

The SX can sometimes latch up and consume more than 150mA and get very warm even though all the IO pins are not allowed to source or sink any currents more than 5mA.

This can happen if

1. The 5V regulator lead has a dry solder and you wiggle it with your finger.
2. After programming the SX with SX-Key, you just pull out the SX-Key with the power still on.

I found out today that the watchdog can reset and recover the SX20AC/SS even though it is very hot and latched up at 160mA.

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Comments

  • Guenther DaubachGuenther Daubach Posts: 1,321
    edited 2008-02-03 14:44
    Hmmm...

    Patient to doctor: "When I press here, it hurts". Doctor to patient: "Then don't press there".

    Both situations you describe are irregular: The power supply should not bounce on and off, and it is always a good idea to pull or plug on the SX-Key with the system powered down before.

    I don't know the SX internals in detail, so I can explain this effect only on my assumptions: Either does the SX enter into some indifferent state where some high- and low-end output drivers are both on, or - maybe - it operates at a very high clock frequency on some overtone of the attached resonator/xtal.

    BTW: I never saw such a latchup here, and I've used over 1000 SXes for my various projects so far.

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    Greetings from Germany,

    G
  • dkemppaidkemppai Posts: 315
    edited 2008-02-05 19:49
    william chan said...
    I wonder if anybody has seen this before.
    This latch-up problem is always there since many years ago.

    The SX can sometimes latch up and consume more than 150mA and get very warm even though all the IO pins are not allowed to source or sink any currents more than 5mA.

    This can happen if

    1. The 5V regulator lead has a dry solder and you wiggle it with your finger.
    2. After programming the SX with SX-Key, you just pull out the SX-Key with the power still on.

    I found out today that the watchdog can reset and recover the SX20AC/SS even though it is very hot and latched up at 160mA.

    I've seen It happen too!·Had a few SX's burn my finger tips!

    I had to reprogram mine to get them to work again. The only way to do this was to remove power, hook up the Key, and plug power in and very quickly mash down on the program button...···· Once the programming was initiated, the current draw fell to normal programming currents.

    -Dan

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    "A saint-like quantity of patience is a help, if this is unavailable, a salty vocabulary works nearly as well." - A. S. Weaver
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