Fairchild Introduces the Industry’s Smallest Low-Ohmic Analog Switches

South Portland, Maine ” Fairchild Semiconductor, the fastest growing supplier of analog switch solutions (source: Selantek), announces three new low-Ohmic analog switch products”the FSA4157 Single Pole/Double Throw (SPDT), FSA1156 Normally Open Single Pole/Single Throw (SPST NO) and the FSA1157 Normally Closed Single Pole/Single Throw (SPST NC) switches.

The devices' low ON Resistance (RON) improves signal integrity and lowers the drive necessary to support audio and signal processing applications. Available in chip-scale MicroPak packaging, all products offer greater than 65% space savings over traditional SC70 and SOT-23 packages, as well as:

Low ON Resistance (RON)”maximum of 1.0 to 1.35 Ohms

Broad operating voltage range”1.65 to 5.5V
Low THD”0.002% typical
Low RON Flatness”0.2 Ohm typical

By design, Fairchild's analog switches incorporate features that are important to a wide range of customers and applications. These universal switches make selection simpler, reduce qualification and inventory costs, and provide superior performance for easy re-use in system upgrades. The wide 1.65″5.5V operating range of these devices provides the added benefit of protecting cell phone batteries from damage caused by overcharges. The higher operating voltage of the Fairchild switches enables them to easily accommodate overcharges of up to 4.6V, which typical 3.3V-rated analog switches cannot do. The greater than 350MHz bandwidth of the Fairchild devices supports high-speed analog and digital signal routing in low-voltage applications, while providing industry-leading ESD protection of better than 7500V (HBM).

“The extremely low Total Harmonic Distortion ensures that the signal integrity is not degraded by the switch, preserving the quality of the audio signal. Coupled with flat RON characteristics and small packaging, these switches offer designers a real value advantage in space-constrained portable applications,” says Jeff Ju, applications engineer for analog switches.

The low-Ohmic analog switches add to Fairchild's portfolio of products targeting portable applications. These products include audio amplifiers, LED drivers and LEDs for backlighting, supervisory products such as temperature sensors and reset generator circuits, and DC/DC conversion products such as DC/DC converters, LDOs and MOSFETs.

These lead-free (Pb-free) products meet or exceed the requirements of the joint IPC/JEDEC standard J-STD-020B and are compliant with the European Union requirements, which will take effect in 2005.


FSA4157, $0.45 each (1000 pcs) in 6-lead SC70 or Chip-scale MicroPak
FSA1156, $0.38 each (1000 pcs) in 6-lead SC70 or Chip-scale MicroPak
FSA1157, $0.38 each (1000 pcs) in 6-lead SC70 or Chip-scale MicroPak
Availability: Now
Delivery: 4 weeks ARO

Editor's Note: For information about these products, go to:



For information on other Fairchild products, design tools and sales contacts, please visit

Fairchild Semiconductor is admittedly doing a “come-from-behind” in the dormant analog switch market. The territory has been well carved by competitors like Maxim, Vishay Siliconix and Analog Devices. But that shouldn't mean there isn't room for a well-engineered and carefully targeted product. Fairchild has been sticking its toe into the switch market for years; its latest publicized entry was an SPST device with TTL-level control. For a company like Fairchild, the people associated with a new product line could feel like they're working in a startup company. Imagine the elation: Any growth could feel like 100 percent – or 170 percent for the switch line (at least, according to Selantek).

This shift into a number four position has encouraged Fairchild to go deeper into a market it believes will be about $275 million in 2007. It has begun to explore the specific application needs of mobile phones, computers, industrial and medical equipment. Cell phones currently make up over 50 percent of the total market, observes Paul Kierstead, Fairchild's newly-promoted director marketing. “The ultra-portable market currently offers a tremendous opportunity,” he says. “Space and power are the two greatest concerns in this segment.”

This not to underestimate the role of switching speeds and configurations, the on-resistance and bandwidth of the switch. As a Fairchild competitor suggested in a recent Planet Analog feature, analog switches are based on parallel p-channel and n-channel FETs. The parallel connection supports rail-to-rail operation and lowers the on-resistance. But, unless the devices are perfectly matched, it won't be zero. Thus, you're always looking at tradeoffs between turn-on thresholds, bandwidth and power consumption (see Catherine Redmond, “Low on-resistance, one key for the perfect switch”).

We've got a lot of evidence to suggest that Fairchild has done its homework on these new devices. Previously introduced devices like the FSA3157 SPDT switch provides the means to switch between a headphone and internal speaker in cellular handsets. The FSA66 SPST switch is used in multi-mode mobile phones – between the transceiver and baseband components – to switch between DCS1800 and GSM900 bands. The FSAV330 (Quad SPDT) video switch allows computer designers to switch between multiple video signals (like separate RGB lines).

The new products are optimized for very low on-resistance (slightly more than one-ohm) compared to 5.0 ohms for many current products. (Lower RON reduces the power necessary to drive a cellphone or PDA speaker, Paul Kierstead reminds.)

The on-resistance, remember, is also frequency dependent. Fairchild's device boasts a “flatness” (RFLAT) of 0.2 ohms (compared to 6.0 ohms for current standards). A smaller RON flatness is needed to minimize THD especially for audio systems with very small impedance loads. Thus, these switches boats a 0.002% Total Harmonic Distortion (THD) figure – a 5x improvement over the 0.011% for current standards. (Lower THD is needed to keep the fidelity or high quality of audio signals).

Finally, the ESD performance is 7500V – well above the 2000V industry standard. This provides superior protection against external transients.

The new devices include the FSA4157b, a single SPDT; the FSA1156 Single SPST normally-open and the FSA1157 Single SPDT (NC). Their introduction is perhaps intended to put the current champions of the analog switch market on notice: In this environment, you can either heed Satchel Paige's now timely advice and/or… continue to play like the Yankees.

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