Analogue switch protects from negative vibes

Fairchild Semiconductor has developed an SPDT analogue switch that protects ASICs, microprocessors and other ICs from damage caused by negative voltage transients.

Fairchild Semiconductor has developed an SPDT analogue switch that protects ASICs, microprocessors and other ICs from damage caused by negative voltage transients.

The NC7SBU3157 single-pole, double-throw switch protects internal ICs from noise or undershoot events whenever a connector is inserted into an MP3 player, CD player, notebook, mobile phone, or any other device with an analogue or digital signal connector.

The NC7SBU3157 low voltage SPDT analogue switch with -2V undershoot protection incorporates Fairchild's patented undershoot hardened circuitry (UHC).

This feature allows audio-electronics designers to eliminate the negative-voltage transient that occurs when an audio jack and plug are connected, which causes damage to an ASIC or microprocessor that lacks robust protection from low-voltage high-current events.

"The NC7SBU3157 protects ICs from undershoot transients, regardless of frequency, down to -2V", explains Seth Prentice, Fairchild's switch product marketing engineer.

"Older electronics used bulky capacitors, inductors and resistors to absorb this kind of energy.

Yet newer compact designs containing ASICs lack robust protection circuitry and are easily damaged.

Attempts to protect them using Schottky diodes are ineffective as they protect only against high-voltage, low-current events, such as ESD.

Likewise, attempts using low-pass filters protect against events only at a predetermined frequency".

"Manufacturers of MP3 and CD players can easily improve quality and customer satisfaction by designing in circuit protection with components such as the NC7SBU3157 switch", claims Prentice.

"Designs using undershoot protection when switching from a speaker to a headphone will prevent damage to an expensive ASIC or microprocessor IC each time a user inserts an audio jack in to a player".

Designed for high bandwidth, the SPDT analogue switch passes signals of over 250MHz to permit versatile routing of analogue signals as well as digital signals with minimal propagation delay.

It has low 5ohm on-resistance, operates rail-to-rail over a 1.65-5.5V supply range, and features low 0.001% total harmonic distortion.

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