Device latchup

Dear Rani,

A latchup is a type of short circuit, normally occurs in an improperly designed IC. As we know in CMOS technology, there are a number of instrinsic BJT, and in CMOS processes, these BJTs may create problems when the combination between n-well and p-well andsubstrate rsults in the formation of parasitic n-p-n-p structures.If these  parasitic structure are triggered which will lead to a short of the Vdd and GND lines, usually resulting in destruction of the chip, or a system failure that can only be resolved by power-down

The figure below is a schematic about parasistic transistors in a CMOS circuit. A p-n-p-n structure acts as a PNP and an NPN transistor stacled next to each other. During a latchup, when one of the transistor is conducting, the other one begins conduction as well. They keep each other in saturation for as long as the structure is forward-biased and some current flows through it, that normally means until a power-down.

The latchup can happen at any place where the required parasitic structure exists. The causes of latchup are multiple, a spike of positive or negative voltage on an input or output pin, or the supply voltage exceeding the absolute maximum ration etc.

The link below is a TI Application Note about latchup:

http://www.ti.com/general/docs/lit/getliterature.tsp?baseLiteratureNumber=SLYA014&fileType=pdf

Talking about whether a latchup will cause a permanent broken-down to a device, I think it's hard to say. It depands on whether latchup is just causing a simple short or damages some electronic elements. You can try to re- power the device for making sure whether it can be recovered.

Best Regards

Na