Latchup

Latchup

A latchup is the inadvertent creation of a low-impedance path between the power supply rails of an electronic component, triggering a parasitic structure, which then acts as a short circuit, disrupting proper functioning of the part and possibly even leading to its destruction due to overcurrent. A power cycle is required to correct this situation.

The parasitic structure is usually equivalent to a thyristor (or SCR), a PNPN structure which acts as a PNP and an NPN transistor stacked next to each other. During a latchup when one of the transistors is conducting, the other one begins conducting too. They both keep each other in saturation for as long as the structure is forward-biased and some current flows through it - which usually means until a power-down. The SCR parasitic structure is formed as a part of the totem-pole PMOS and NMOS transistor pair on the output drivers of the gates.

The latchup does not have to happen between the power rails; it can happen at any place where the required parasitic structure exists. A spike of positive or negative voltage on an input or output pin of a digital chip, exceeding the rail voltage by more than a diode drop, is a common cause of latchup. Another cause is the supply voltage exceeding the absolute maximum rating, often from a transient spike in the power supply, leading to a breakdown of some internal junction. This frequently happens in circuits which use multiple supply voltages that do not come up in the proper order after a power-up, leading to voltages on data lines exceeding the input rating of parts that have not yet reached a nominal supply voltage.

Yet another common cause of latchups is ionizing radiation.

It is possible to design chips that are latchup-resistant, where a layer of insulating oxide (called a "trench") surrounds both the NMOS and the PMOS transistors. This breaks the parasitic SCR structure between these transistors. Such parts are important in the cases where the proper sequencing of power and signals cannot be guaranteed (e.g., in hot swap devices). Most silicon-on-insulator devices are inherently latchup-resistant.

Another possibility for a latchup prevention is the "Latchup Protection Technology" circuit. When a latchup is detected, the LPT circuit shuts down the chip and holds it powered-down for a preset time.

Testing for Latchup

* See EIA/JEDEC STANDARD IC Latch-Up Test EIA/JESD78.
This standard is commonly referenced in IC qualification specifications.

See also

* Electrostatic discharge: For qualification testing of semiconductor devices, ESD and latchup are commonly considered together.

External links

* [http://www.ece.drexel.edu/courses/ECE-E431/latch-up/latch-up.html Latch-up in CMOS designs]
* [http://www.analog.com/library/analogDialogue/archives/35-05/latchup/ Analog Devices: Winning the battle against latchup in CMOS analog devices]
* [http://www.nasatech.com/Briefs/July98/0798ETB2.html Single-event latchup protection of integrated circuits]
* [http://www.maxwell.com/microelectronics/products/technologies/lpt_overview.html Maxwell Technologies Microelectronics: Latchup Protection Technology]
* [http://www.whitemountainlabs.com/latchup.aspx Latch Up Overview]


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Look at other dictionaries:

  • Latchup — Der Fachbegriff Latch Up (englisch Single Event Latch Up; abgekürzt SEL) bezeichnet in der Elektronik den Übergang eines Halbleiterbauelements, wie beispielsweise in einer CMOS Stufe, in einen niederohmigen Zustand, der zu einem elektrischen… …   Deutsch Wikipedia

  • Latchup — užsklendimas statusas T sritis radioelektronika atitikmenys: angl. latchup vok. Einklinken, n; Einschnappen, n; Latchup, n rus. защёлкивание, n; фиксирование, n pranc. captage, m; capture, f …   Radioelektronikos terminų žodynas

  • latchup — užsklendimas statusas T sritis radioelektronika atitikmenys: angl. latchup vok. Einklinken, n; Einschnappen, n; Latchup, n rus. защёлкивание, n; фиксирование, n pranc. captage, m; capture, f …   Radioelektronikos terminų žodynas

  • Latchup-Einschalten — užsklendžiamasis įsijungimas statusas T sritis radioelektronika atitikmenys: angl. latchup turn on vok. Latchup Einschalten, n rus. защёлкивающее включение, n pranc. mise en circuit par capture, f …   Radioelektronikos terminų žodynas

  • latchup turn-on — užsklendžiamasis įsijungimas statusas T sritis radioelektronika atitikmenys: angl. latchup turn on vok. Latchup Einschalten, n rus. защёлкивающее включение, n pranc. mise en circuit par capture, f …   Radioelektronikos terminų žodynas

  • latchup-free CMOS device — jungtinis nefiksuojamojo perjungimo MOP įtaisas statusas T sritis radioelektronika atitikmenys: angl. latchup free CMOS device vok. latchupfreier CMOS Baustein, m; latchupfreier komplementärer MOS Baustein, m rus. КМОП прибор без защёлкивания, m… …   Radioelektronikos terminų žodynas

  • Single Event Latchup — Der Fachbegriff Latch Up (englisch Single Event Latch Up; abgekürzt SEL) bezeichnet in der Elektronik den Übergang eines Halbleiterbauelements, wie beispielsweise in einer CMOS Stufe, in einen niederohmigen Zustand, der zu einem elektrischen… …   Deutsch Wikipedia

  • complementary MOS latchup — jungtinio MOP darinio užsidarymas statusas T sritis radioelektronika atitikmenys: angl. complementary MOS latchup vok. Lach up Effekt in komplementären MOS Strukturen, m; Thyristoreffekt in komplementären MOS Strukturen, m rus. защёлкивание КМОП… …   Radioelektronikos terminų žodynas

  • Latch-up — Latchup es un termino usado en el mundo de los circuitos integrados (microchips)para describir un tipo particular de cortocircuito que puede ocurrir en un circuito eléctrico mal diseñado. Mas específicamente es la creación inadvertida de una… …   Wikipedia Español

  • Radiation hardening — is a method of designing and testing electronic components and systems to make them resistant to damage or malfunctions caused by ionizing radiation (particle radiation and high energy electromagnetic radiation),[1] such as would be encountered… …   Wikipedia

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