----- Original Message -----From: Valerij AvrealijTo: Leon HellerSent: Sunday, February 13, 2005 12:56 PMSubject: Re: [AVR-Chat] ISP problem: very high current when ISP switched ON (more 200mA)
Hello, Leon.
You wrote:
> With CMOS devices, it is possible in some situations for the substrate to
> become biased so that the device behaves like an SCR, think of a
> forward-biased diode. Lots of current is drawn and the device can
> self-destruct. If power is removed quickly, they often recover.
> It can be caused by applying a voltage to an I/O pin before the chip is
> supplied with power, and there are several other causes:
> http://www.analog.com/library/analogDialogue/archives/35-05/latchup/
Very interesting effect. How it can be overcomed?
Just follow the suggestions in the article, and search for other material with Google. It might not be the cause of your problem, of course; I haven't found AVRs particularly prone to it. Many years ago, the Immos transputer often latched up if one touched the top of the package whilst the chip was running - static on the metallised top (it wasn't grounded) would start it off. They always recovered, I found.
You wrote:
> With CMOS devices, it is possible in some situations for the substrate to
> become biased so that the device behaves like an SCR, think of a
> forward-biased diode. Lots of current is drawn and the device can
> self-destruct. If power is removed quickly, they often recover.
> It can be caused by applying a voltage to an I/O pin before the chip is
> supplied with power, and there are several other causes:
> http://www.analog.com/library/analogDialogue/archives/35-05/latchup/
Very interesting effect. How it can be overcomed?
Just follow the suggestions in the article, and search for other material with Google. It might not be the cause of your problem, of course; I haven't found AVRs particularly prone to it. Many years ago, the Immos transputer often latched up if one touched the top of the package whilst the chip was running - static on the metallised top (it wasn't grounded) would start it off. They always recovered, I found.
Leon
--
Leon Heller, G1HSM
http://www.geocities.com/leon_heller
http://www.geocities.com/leon_heller