Isolation of digital signals is needed for a wide range of reasons: signal integrity, floating grounds, separating high- and low-voltage signals, and user safety. It’s a requirement in automotive designs that just a few decades ago didn’t need it, or were served by low-speed electromechanical relays that, of course, are inadequate for isolating today’s data links. While there are various all-electronic and thus high-speed options for data isolation, doing so in a small wide-temperature package is definitely a challenge.
To address these needs, Texas Instruments introduced what it says is the industry’s first digital isolator qualified to the “Grade 0” ambient operating temperature specification of the Automotive Electronics Council (AEC)-Q100 standard. Designed to protect low-voltage circuitry from high-voltage “events” in hybrid-electric-vehicle (HEV) and electric-vehicle (EV) systems, the 100-Mb/s ISO7741E-Q1 quad-channel isolator uses SiO2-based capacitive-coupling techniques to achieve 1.5-kVRMS working voltage with 5000 VRMS isolation ratings per UL 1577 (Fig. 1).
The isolator supports temperatures up to the Grade 0 maximum mandate of 150°C. Thus, it eliminates the need to design and implement additional cooling systems to reduce operating temperatures to below 125°C, which is the maximum temperature that devices qualified only to Grade 1 can support.
The multichannel isolator operates from a wide supply range of +2.25 to 5.5 V, providing level translation between those two voltages. Other electrical ruggedness ratings include up to 12.8-kV surge-withstand capability along with a ±100-kV/μs typical common‐mode transient immunity (CMTI) rating. Power consumption is 1.5 mA per channel at 1 Mb/s while propagation delay is 10.7 ns (both typical) with a 5-V supply.
The comprehensive 34-page ISO7441E-Q1 datasheet provides a full array of static, dynamic, temperature-dependent, and voltage-dependent characterizations and graphs. Despite its fairly high voltage ratings, the device is housed in 10.3- × 7.5-mm, 16-lead SOIC package, and is priced at US$1.49 in 1,000-unit quantities.
Of course, isolation of a data link alone solves only part of the end-to-end design problem. To provide Controller Area Network with Flexible Data-Rate (CAN FD) communications, TI also introduced the TCAN1044EV-Q1, which is rated for Grade 0 150°C temperature operation as well (Fig. 2).
This high-speed transceiver meets the physical-layer requirements of the ISO11898-2:2016 high-speed CAN specification and supports both classical CAN and CAN FD networks up to 8 Mb/s. It’s available in an 8-lead, 4.90- × 3.91-mm SOIC for US$0.43 in 1,000-unit quantities and has a detailed datasheet, too.
More information on AEC-Q100 automotive temperature grades and why Grade 0 is critical for in-vehicle network signal isolation can be found in the TI blog, “Solving high-temperature isolation design challenges with Grade 0 digital isolators”; TI’s capacitive-isolation technology is also discussed in its “Capacitive Isolation Technology” posting.