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USB accessory switch saves space in portable apps

Posted: 15 Oct 2009     Print Version  Bookmark and Share

Keywords:USB  switch  UART  mobile phone 

FSA800 USB switch

Fairchild Semiconductor has released the smallest USB accessory switch with built-in charger detection that integrates all of the key multimedia functionality into a low-profile package.

The FSA800 offers designers of mobile phones, PDAs and MP3 players a simplified, reduced component count solution for portable designs.

The device, which is packaged in a low-profile UMLP (1.8mm x 2.6mm x 0.55mm), offers built-in charger detection, 28V of over-voltage tolerance, built-in termination resistors and negative swing capability.

The FSA800 includes a built-in charger detection, eliminating the need to add a bias resistor into the design. The device is also capable of handling USB data, stereo and mono audio, microphone and UART data all on a common connector port and is touted to be the only switch able to handle microphone data.

In addition, the device features low capacitance (7pf), allowing data to move swiftly along the signal path.

It also packs built-in termination resistors that eliminate the pop noise that frequently happens when plugging in an audio jack in a cell phone or MP3 player. Meanwhile the 28V over-voltage tolerance on the VBUS pin ensures robust protection against high voltage events. The FSA800 also offers negative swing capability so that audio signals can swing below ground, eliminating the need for an additional bias resistor. Many alternate solutions do not have this capability and a bias resistor must be added into the design.

According to Fairchild, mobile phone manufacturers are moving to implement a micro-USB connector for both charging and audio and data transmission. Citing recommendations from the Open Mobile Terminal Platform, the company anticipates the mobile phone industry will adopt a common charging standard which require the micro-USB port supporting USB, audio, charging and other capabilities. Fairchild predicts that all accessories will pass through a single 5-pin micro-USB connector which allows for slimmer overall designs of portable devices.

"We are introducing the new product because have a strong belief that this is what the market is going to require. We see a trend for designers to implement a unique micro-USB for all the functions," explained Aranzazu Diaz Valdivieso, Fairchild's European product marketing manager for signal path products. "We already have real customer requests. The customers are asking us for such a device because it is the way they want to implement the next platform."

Outlining the design challenge posed by the micro-USB trend, Valdivieso said: "We see the need to make the design more compact. To help simplify the design of the mobile phone and to ensure that a solution will be provide with a small number of components and a small size you will provide a good charging procedure, a good audio signal because it is very important that the audio signal has high quality in multimedia phones and everything is achieved using one small part compared with a traditional multi-component approach."

He added that when implementing devices like the FSA800, designers are able to save a lot of components. "There are main five components that can be saved. When you want to drive all the signals from the micro-USB port you need three different 2:1 switches to switch between the audio, the microphone signal, the UART or the full speed USB and the high speed USB. Plus you also need a switch control device to control the three switches and you also need a charger detection device to detect when the charging event is happening and to stop the other kind of signals flowing through the USB. You actually also need an over voltage tolerance, OVT, device to protect the whole circuitry from unexpected peak swings when charging the device. The FSA800 addresses all these design issues."

A key driver for the micro-USB technology will be the desire for users to no longer need multiple charging devices. Valdivieso explained: "With the FSA800 users will benefit from having a universal connector for charging. This means they will not have to throw away the charger every time they buy a new mobile phone. The user will save money on chargers and it will also be environmentally friendly because there will be less electrical waste. It will also be more convenient because users will be able to charge their mobile phone through the USB port so you will not need to use a charger all the time. You can have the option of charging it through your laptop."

The FSA800 is part of a portfolio of Fairchild's USB solutions that are ideal for USB port isolation, connector sharing and signal multiplexing. The switches are often used to share or route USB ports and to isolate flash memory/uDisc removable devices. The switches are designed to be compliant with USB2.0 Full Speed and Hi-Speed with bandwidths in excess of 720MHz.

Samples of the FSA800 are available now with a six weeks lead time for delivery. The price is Rs.34.17 ($0.70) each in 1,000 pieces.

- Paul Buckley
Power Management DesignLine Europe





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