Abstract

Further information on device operation is available in the ISO1228 Eight-Channel Isolated Digital Input with Current Limit and Diagnostics, data sheet and ISO1228DFBEVM EVM. This guide is used to explain the performance benefits of serial and parallel mode and how to switch dynamically between modes for the best functionality.

24V digital input systems have a growing need to support higher channel density and to integrate various features (Space-Saving Design Techniques for Multichannel High- Voltage Digital Input Modules). The ISO1228 address both needs as an eight-channel isolated 24V digital input receiver that can use a serial (SPI) or a parallel digital output mode to control various integrated digital features such as: wire-break detection, in-built glitch filters, field-side supply monitoring and built-in CRC across the isolation barrier. Additionally, designers can use the serial mode to monitor the inputs over SPI and reduce the number of pins in an MCU. The isolated logic side can range from 1.71V to 5.5V, supporting 1.8V, 2.5V, 3.3V, and 5V controllers. The field side supply voltage can range from 8.5V to 36V in sink mode and 13V to 36V in source mode. ISO1228 supports data rates up to 1.5Mbps, and can pass a minimum pulse width of 667ns for high-speed operation.

The ISO1228 is designed to comply with the IEC 61131-2 standard for digital inputs and supports eight channels with IEC 61131-2 Type 1, and 3 characteristics or four channels with Type 2 characteristics. The ISO1228 also includes integrated resistor-programmable current limiting and field side, input-current-powered LED indication to reduce the system's power dissipation and board temperature. ISO1228 can be configured for either sourcing or sinking type digital inputs with minimal hardware changes. The ISO1228 also supports IEC ESD and surge protection to achieve a robust design.