Shop OBEX P1 Docs P2 Docs Learn Events
SX28DP Burned...Yes, burned like on fire. — Parallax Forums

SX28DP Burned...Yes, burned like on fire.

prozachprozach Posts: 11
edited 2010-01-20 22:04 in General Discussion
I have several of these chips out on projects and I just received one back that looks like the chip caught on fire!· Has anyone had this happen before?

My main question is what might of caused this.· I have the board running off an ATX power supply so the 5v is rated at 30amps.· I have a 1 amp fuse to protect from shorts but it was not blown.

After looking at the design in more detail (I did not lay out the board) , I noticed the inputs do not have a current limiting resistor.· One input goes directly to the 5v through a normally closed switch so it receives a direct 5v.· Is a resistor needed?·If so,·might this be the culprit?

Thanks for any help.

zach·

Comments

  • Mike GreenMike Green Posts: 23,101
    edited 2010-01-18 16:38
    The I/O pins of an SX (like those of most microcontrollers) can function as both inputs and outputs. If configured as an input, it could be connected directly to +5V without a current limiting resistor (since there's only microAmps of current involved). If it's configured accidentally as an low output, you would have a "short circuit" between the +5V and ground through the output transistor of the I/O pin circuitry. A current limiting resistor would protect the I/O pin against damage from this sort of situation. Without the resistor, the output transistor would likely overheat and become damaged. The amount of current involved is small, perhaps 30mA to 50mA, not enough to do anything other than damage the output transistor itself and perhaps some of the metallization around it on the chip. It would not cause enough heating of the chip to look like it caught fire. Even if the chip were connected in reverse to the power supply which would cause massive damage to the chip, I doubt that you'd get enough heating to look like fire damage, particularly with a 1A fuse. The chip would get quite hot, too hot to touch, but not charring. If the fuse had a higher rating, that might be possible. Several Amps of current would cause that much heat.
  • Guenther DaubachGuenther Daubach Posts: 1,321
    edited 2010-01-20 18:58
    Hi,

    please have a look at this thread: http://forums.parallax.com/showthread.php?p=466126

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Greetings from Germany,

    G
  • LeonLeon Posts: 7,620
    edited 2010-01-20 22:04
    I had an SX28 go into CMOS latchup some years ago, I don't think it survived. More modern chips are less susceptible to it.

    Leon

    ▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔▔
    Amateur radio callsign: G1HSM
Sign In or Register to comment.