A digital isolator transfers digital signals across a galvanic isolation barrier, allowing two electrical domains to communicate without a direct electrical connection. Texas Instruments’ TI Precision Labs lesson explains three ways isolators encode that signal transfer: capacitive coupling, edge-based signaling and on-off keying (OOK).
What TI Precision Labs covers
Texas Instruments’ “What is a digital isolator?” lesson is part of its Precision Labs Isolation series. The video, published March 4, 2020, runs 12 minutes and 11 seconds. It introduces the device, explains capacitive, edge-based and OOK isolation, and discusses practical considerations for using a digital isolator.
How a digital isolator transfers a signal
A digital isolator conveys information across a barrier while maintaining galvanic separation between the two sides. The signal must therefore be represented in a form that can cross the barrier without creating a direct conductive path. TI’s lesson discusses three implementation approaches:
- Capacitive isolation: transfers encoded signal changes across a capacitive barrier.
- Edge-based isolation: communicates transitions in the digital signal across the barrier.
- On-off keying (OOK): represents information using changes between signal-on and signal-off states.
These are different ways to carry digital information across an isolation barrier; they do not remove the need to check whether a particular device meets the electrical and regulatory requirements of the end equipment.
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Basic versus reinforced isolation
Basic and reinforced isolation are design categories relevant to the safety requirements of the equipment. The required category depends on the applicable product standard and the system’s voltage and protection scheme; the device family name alone does not establish suitability.
TI’s selection guidance uses 3,000 VRMS as an example threshold for basic isolation and 5,000 VRMS as an example for designs needing higher isolation withstand capability. These are selection examples, not universal definitions of the two categories. Confirm the ratings and approvals for the specific part against the end-equipment standard.
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How to choose a digital isolator
Start with the applicable safety standard and electrical environment, then compare candidate devices against the requirements below. TI’s selection article, “How to select a digital isolator”, describes these factors and the TI families that target different use cases.
1. Check isolation ratings
- Isolation withstand voltage (VISO): the voltage the device can withstand without breakdown under the specified test condition. TI describes a test duration of at least 60 seconds; check the individual device datasheet for the precise method and rating.
- Working voltage (VIOWM): the continuous voltage the isolation barrier is designed to withstand over the product’s life. Required working voltage depends on system conditions, including package, pollution degree and material group.
- Surge isolation (VIOSM): assess the transient surge the barrier must tolerate. TI notes reinforced-isolation applications may call for surge capability above 10 kV; determine the actual requirement from the system standard and environment.
2. Verify creepage and clearance
Creepage is the distance along an insulating surface between conductive parts; clearance is the shortest distance through air. Required spacing varies with the system standard, voltage, package and other conditions. TI gives 4 mm and 8 mm as examples of possible requirements, not universal minimums. A larger package may provide greater spacing and higher isolation capability, while a smaller package can save board area when it still satisfies the applicable rules.
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- Compact Design saves 40% more PCB space compared to photoelectric isolators, making the ADUM1201ARZ a perfect fit for space-constrained designs in RS-232, RS-422, and RS-485 transceiver isolation.
- Bi-Directional Communication with two isolated channels, the ADUM1201ARZ provides minimal crosstalk and is ideal for versatile applications, including SPI and CAN bus transceiver signal isolation.
3. Consider common-mode transient immunity
Common-mode transient immunity (CMTI) describes a device’s ability to maintain correct signal behavior during rapid voltage changes common to both sides of the barrier. High CMTI can matter in electrically noisy environments such as motor drives and solar inverters, where a bit error may have serious consequences. Compare the actual device specification with the transients expected in the application.
4. Match speed and power to the system
Choose a data rate that supports the signaling protocol and its timing requirements. TI’s family guidance includes a 150-Mbps example in the ISO76xx high-speed range. That example is not a guarantee for every part in the family; check the specific datasheet. For battery-powered or loop-powered designs, power consumption may be a more important constraint than peak speed.
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5. Check channels, direction and fail-safe behavior
After the electrical requirements are met, compare channel count and direction, package, operating temperature and regulatory qualification. Also verify whether an output defaults high or low when its input is absent or the device is unpowered, and ensure that behavior is safe for the circuit.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.TI digital-isolator families in the selection article
TI’s family descriptions below are broad positioning guidance from its selection article, not a substitute for checking a specific part’s current datasheet, approvals and availability.
| Family | TI’s stated focus |
|---|---|
| ISO67xx | Basic and reinforced isolation for cost-sensitive applications |
| ISO77xx | Basic and reinforced digital isolators |
| ISO78xx | Highest isolation rating and widest creepage and clearance in the article’s family comparison |
| ISO70xx | Ultra-low-power digital isolators |
| ISO73xx | Low-power, low-jitter digital isolators |
| ISO76xx | High-speed isolation; the article gives a 150-Mbps example |
| ISOS141-SEP | Radiation-tolerant digital isolator |
How to narrow ISO77xx and ISO78xx choices
The family labels do not identify a universally best part. Use the end-equipment standard and electrical requirements to decide whether the higher isolation and spacing described for ISO78xx are needed, or whether an ISO77xx part meets the requirements. Then compare individual datasheets for VISO, VIOWM, VIOSM, creepage and clearance, CMTI, channels and direction, data rate, power, fail-safe state, temperature range and regulatory qualification.
TI’s family comparison does not establish live stock, pricing or lifecycle status for individual devices. Confirm those details with TI or an authorized distributor before designing around a part.
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