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Single occasion upset and restoration

The consequences of cosmic rays have been as soon as mentioned in “Doubled-up MOSFETs“.

The concept was that part redundancy, paired MOSFETs in that case, would permit one MOSFET to nonetheless perform even when its accomplice in a switched mode energy provide have been to be disabled from regular switching due to a cosmic ray occasion, a single occasion upset, or an SEU (Determine 1).

Determine 1 An SEU from a cosmic ray can result in part failure.

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Nonetheless, an SEU doesn’t essentially have to return from a cosmic ray. CMOS built-in circuits are generally seen to latch-up for no obvious purpose. The latch-up occasion comes about from inner four-layer constructions that look very very similar to SCRs which when triggered, can nearly brief circuit the +Vcc rail pin to floor. In contrast to the facility MOSFET scenario, part redundancy is probably not doable. In such a case, SEU restoration would be the reply.

Determine 2 is conceptual, however it’s derived from precise circuitry that was utilized in a extra complicated design. 

Determine 2 The SEU restoration idea the place the circuitry in inexperienced in latch-up inclined.

The essential thought is that Q1, Q2 etal in inexperienced represents a latch-up inclined built-in circuit, most likely CMOS, whereas V1 etal in blue represents a latch-up set off. An RC pair in yellow gives a delay of the latch-up restoration course of in order that the restoration situation may be extra simply seen on the scope, however we’ll shortly take away that RC pair.

When the IC latches up, it drags down the output of the +5-volt regulator. When that voltage falls beneath the comparator threshold, +3 volts as proven right here, the comparator sends a drive pulse to the facility MOSFET which additional lowers the rail voltage to the place the IC latch can’t be sustained. When the facility MOSFET turns off once more, the +5-volt regulator output voltage returns to regular.

If we now take away that RC delay, the situation proceeds the identical means, however on this simulation all of it occurs too quick for the saturation voltage of the latched-up system to be viewable within the scope show (Determine 3).

Determine 3 SEU Restoration the place the RC delay is now eliminated.

John Dunn is an electronics marketing consultant, and a graduate of The Polytechnic Institute of Brooklyn (BSEE) and of New York College (MSEE).

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