October 2009

Doc ID 16144 Rev 1

1/28

AN3031

Application note

SCLT3-8 input termination demonstration board

STEVAL-IFP007V1

1

Introduction

The SCLT3-8BT8 is an eight channel termination used for interfacing automation digital

inputs. It is designed for 24 VDC applications and meets type 3 input characteristics in

accordance with IEC 61131-2 (programmable controllers international standard). The chip

integrates an SPI peripheral output for communication with logic/ASIC/microcontroller. Its

structure allows the transfer not only of the data but also of additional information including

thermal alarm, undervoltage indication and parity bits. It is particularly beneficial for

applications with high channel counts. The serial communication allows for reduction of the

number of lines, which in most applications need to be galvanically isolated.

The device optimizes the input VI characteristic shape to reduce power dissipation. This

becomes critical when the application enclosure requires higher protection levels, such as

IP codes IP65 and IP67. These closed cabinets are used in various automated lines,

including the food industry. The power dissipated inside the module is very limited, as there

is usually no air circulation inside the box. The current limitation also reduces power losses

on the sensor side.

Another important parameter is electrical protection and susceptibility of the application.

The SCLT3-8BT8 implements large protection diodes on each input and supply voltage line.

Serial resistors ensure a higher level of susceptibility than required.

Thanks to its compact package, an SCLT3-8BT8 application occupies little space on the

PCB compared to discrete solutions.

Figure 1.

STEVAL-IFP007V1 demonstration board

www.st.com