Despite the benefits of large-scale integration for mixed-signal functions, there’s still an important role for optimized, limited-function analog components that do one or two things, do them very well, and then “step aside” without attempting to also implement other system functions. By confining themselves to primarily analog needs, they don’t have the compromises that inevitably result from using a mostly digital process for analog signals.
This is demonstrated by Texas Instruments' ISO224, a reinforced isolation amplifier that combines high precision with additional internal design attributes to increase voltage rating, extend temperature rating, and lengthen operating life (see figure). It’s available in two versions: the higher-grade ISO224B and lower-grade ISO224A.
The detailed internal block diagram shows the delta-sigma modulator, double-capacitive isolation, and complementary demodulation blocks of the ISO224 device.
The ISO224 is certified to provide reinforced galvanic isolation of up to 5 kVRMS, with a double-capacitive isolation barrier that also provides a high level of magnetic field immunity. Despite its higher rating, it comes in a package that’s 60% smaller than the previous-generation ISO12x amplifiers. Target applications include factory automation and control, grid infrastructure, rail transport, and motor-drive applications, all well known for electrically and thermally stressful conditions.
The ISO224’s working isolation voltage of 1500 VRMS is 50% higher than required by isolation-industry standards. The ISO224B features common-mode transient immunity (CMTI) of up to 80/140 kV/µs (minimum/typical) and 15 kV/µs for the ISO224A, isolation transient overvoltage (ITO) rating of 7000 V, and operation over an extended industrial temperature range of −55 to +125°C. Safety-related certifications include 7071-VPEAK Reinforced Isolation per DIN VDE V 0884-11: 2017-01, and 5000-VRMS Isolation for 1 Minute per UL1577.
The analog-input side has a ±12-V range, which is a natural fit for accurate sensing of ±10-V signals. On its output side, the ±4-V output of the ISO224 is compatible with direct connection to an analog-to-digital converter with 5-V input. Critical analog specifications highlighting its precision are shown in the table.
The ISO224 amplifiers do require external power, of course. For the “high side” where the input signal or sensor is connected, it needs an isolated single-ended supply between +4.5 and +18 V. (Note that while providing this isolated power may have been a headache in the past, many tiny, isolated supplies, i.e., converters, are now available from several vendors that make this almost into a non-issue.) The low (output) side requires a single +4.5- to +5.5-V non-isolated supply.
To speed end-product development and design-in, users can download the TINA-TI SPICE model, then simulate and analyze their circuit behavior by downloading the SIM TINA-TI reference design, the ISO224 TINA-TI SPICE model, or by getting “hands-on” with the ISO224 evaluation module. The ISO224 is housed in wide-body 8-pin SOIC measuring 5.85 × 7.5 mm. Pricing starts at US $6.49.
Tom Bonifield , “How High-Voltage Isolation Technology Works – Capacitive Structure” (video)
Tom Bonifield, SSZY028, “Enabling high voltage signal isolation quality and reliability”
Vikas Kumar Thawani and Anand Reghunathan, SLYY112, “Fully integrated signal and power isolation – applications and benefits”