Tiny BGA-style Optocoupler Targets Consumer and Industrial Designs

May 5, 2004 11:35 AM
By David Morrison, Editor, Power Electronics Technology

A BGA-packaged optocoupler from Fairchild Semiconductor offers the smallest form factor for a safety-rated device of this type. The FODB100 Microcoupler, a single-channel optocoupler with a transistor output, features a 3.5-mm × 3.5-mm footprint and stands a maximum of 1.20-mm tall when mounted to the pc board. The Microcoupler is designed for use in consumer products, such as chargers and adapter, as well as industrial applications like power supplies and motor controls.

A further distinction for this part is its -40°C to 125°C operating temperature range. This wide range contrasts with traditional optocouplers, which usually work up to just 100°C. Another key feature is high-current transfer ratio at low input current. Capable of operating with 0.5 mA to 2 mA of drive current, this optocoupler supports operation in products designed for low-standby power.

To achieve its performance, the Microcoupler exploits a unique construction and choice of materials. The device’s two chips (an aluminum gallium arsenide infrared LED and a silicon phototransistor) mount to the bottom side of a BGA substrate and are encapsulated with a dome-shaped covering made of RTV materials. Both the shape of the dome and its composition were chosen to optimize the transfer of optical energy between the chips. The dome consists of a clear inner layer of specially formulated RTV and a reflective outer layer of RTV with titanium oxide.

Current transfer ratio normalized versus temperature for the FODB100 Microcoupler from Fairchild Semiconductor.

Despite the device’s small size, it provides 2.5-kV rms of isolation for 1 s, enabling it to satisfy UL requirements. A second generation of this part with 5.3 kV rms of isolation is being developed to meet European regulatory requirements. To achieve the higher isolation, this optocoupler will need to be almost twice the size of the first version.

The FODB100 is the first in a family of devices that will include dual and multiple channels. Available now, the optocoupler is priced at $0.25 each in quantities of 1000.

For more information, visit www.fairchildsemi.com

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