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Isolators transmit data at up to 150Mbps

Posted: 26 Jan 2006 ?? ?Print Version ?Bookmark and Share

Keywords:Ismini Scouras? Texas Instruments? isolator? ISO721? ISO721M?

TI's on-chip capacitive digital isolators

As industrial automation equipment gets increasingly sophisticated, manufacturers are requiring interface devices that offer faster data rates, as well as higher signal integrity and immunity from magnetic noises. To meet the needs of this steadily growing market, Texas Instruments (TI) developed what it claims is the first on-chip capacitive digital isolatorsthe ISO721 and ISO721Mthat are three times faster than optocouplers, 35 percent faster than high-performance inductive and magnetic coupler devices, and offer up to 60 percent lower power than optical devices.

"The fastest spec we have seen out there is 110Mbps, and we can do 150Mbps," said Ashish Gokhale, TI's isolation product manager, citing the advantages of using capacitive technology versus conventional methods.

Capacitors provide high magnetic immunity like optocouplers, but run faster, he said.

"Fast data rates reduce the latency in the system so you can design a system that doesn't have a lot of wasted bandwidth, which improves efficiency and cost. In some applications where the response time is critical where you're sensing something and need to respond quickly, having a fast data rates helps out quite a bit," Gokhale said.

The ISO721 and ISO721M digital isolators are designed with a silicon oxide insulation barrier that separates the logic input and output buffer, providing a galvanic isolation of up to 4,000V, or 560V of operating voltage. They transmit digital data at up to 150Mb, but block high voltages while keeping out magnetic noises that can distort signal integrity.

The ISO721 (TTL inputs with noise filter) has a signaling rate of 0 to 100Mbps; propagation delay of 17ns; and low jitter, 2ns typical at 100Mbps. The ISO721M (CMOS inputs without filter) has a signaling rate of 0 to 150Mbps; propagation delay of 10ns; and low jitter, 1ns typical at 150Mbps. Both devices support 3V or 5V, and are drop-in replacements for most opto and magnetic isolators.

Fast voltage transients enable the devices to provide high immunity against data corruption. As a result, they can provide a minimum protection level of 25kV/?s.

"We can operate higher and still not corrupt data," he said.

By integrated high-voltage capacitors, TI has sharply reduced the size of the package to an 8-pin SOIC from a 28-pin MSOP, Gokhale said.

The ISO721 and ISO721M digital isolators are manufactured using a BiCMOS process in TI's Dallas facility; the assembly is done in an assembly plant in Taiwan. The parts are single-channel devices, but TI plans to offer dual, triple and quad-channel devices in the future.

The ISO721 and ISO721M digital isolators are already available from TI and the company's authorized distributors. In 1,000-unit quantities, they cost $1.65 each. An evaluation module is also available.

- Ismini Scouras

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Related Datasheets
Part Number Description Category
? ISO721 3.3 V / 5 V High-Speed Digital Isolators (Rev. D) EDA - Embedded Systems Design
? ISO721M 3.3 V / 5 V High-Speed Digital Isolators (Rev. D) EDA - Embedded Systems Design



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