ISO721D 3.3/5V High-Speed Digital Isolators

The design of LED lighting systems for extreme environments must ensure the projected lifetime of the product. This is particularly the case when the power converter is sealed and installed on a streetlight where the cost of replacement or maintenance becomes significant. One of the weak links in an isolated converter is the degradation through time and temperature of the characteristics of the analog optocoupler. Texas Instruments' innovative family of capacitive digital isolators is leading the industry with the best speed and life expectancy.

The ISO721D is a digital isolator with a logic input and output buffer separated by a silicon dioxide (SiO₂) insulation barrier. This barrier provides galvanic isolation of up to 4000 V. Used in conjunction with isolated power supplies, these devices prevent noise currents on a data bus or other circuits from entering the local ground and interfering with or damaging sensitive circuitry.

Overview

A binary input signal is conditioned, translated to a balanced signal, and then differentiated by the capacitive isolation barrier. Across the isolation barrier, a differential comparator receives the logic transition information, and then sets or resets a flip-flop and the output circuit accordingly. A periodic update pulse is sent across the barrier to ensure the proper DC level of the output. If this DC-refresh pulse is not received for more than 4 µs, the input is assumed to be un-powered or not being actively driven and the failsafe circuit drives the output to a logic-high state.