PCLT-2AT4 datasheet(10/18 Pages) STMICROELECTRONICS

10 / 18 page

2 Functional description

PCLT-2A

10/18

Functional description

The PCLT-2A is a dual input termination device designed for 24 V DC automation applications.

It achieves the front-end circuitry of a digital input module (I/O) in industrial automation.

Available in a two channels configuration, it offers a high-density termination by minimizing the

conducting dissipation and the external components count. It is housed in a surface mount

package to reduce the printed board size.

Made of an input voltage protection, a serial current limiting circuit and an output interface, each

channel circuit terminates the connection between the logic input and its associated high side

sensor or switch.

The PCLT-2A is a current limited dual channel circuit compatible with the type 2 (7.5 mA) or

type 3 (3 mA) characteristic of the IEC61131-2 standard. An external resistance RREF allows

the limiting current value to be adjusted from 3 to 7.5 mA.

The unique structure of the PCLT limiter allows its activation threshold to be low and insensitive

to the output voltage up to 2.5 V.

Each input voltage clamping block protects the module input against electromagnetic

interferences such as those described in the IEC61131-2 standard and IEC61000-4-2 (ESD),

4-4 (transient burst), 4-5 (voltage surge) and 4-6 (conducted radio frequency interferences)

standards. The supply input is also designed with such a protection structure.

The current limiting circuit connected between the input and the output pins is compensated all

over the temperature range. Thanks to its low tolerance, the current limitation allows reducing

drastically the dissipation of the input compared to a resistive input. Furthermore, the PCLT2 is

housed into a very low RTH exposed pad TSSOP14 package that allows the PCB cooling pad to

be reduced: the overall module becomes smaller and the hot spot effect is reduced.

The output block of each termination channel transfers the input logic state to a logic output and

a Light Emitting Diode (LED) that allows this state to be checked visually.

2.1

The VMOD pin

The voltage VMOD applied to the selector pin MOD allows the output OUT to be configured

either in an opto-coupler driver for VMOD less than 0.75 V or in a CMOS output able to interface

directly a bus controller circuit for VMOD higher than 2.9 V.

In CMOS mode, the VMOD pin activates a CMOS compatible buffer output, able to source up to

a 50 µA current powered by the MOD pin.

2.2

OFF state

In accordance with IEC61131-2 standard, for both opto-coupler and CMOS configuration

modes when the input current is less than 2 mA (type 2) or 1.5 mA (type 3) the output circuits

divert all the input current and maintain both LED and output in OFF state.

PCLT-2AT4 Datasheet(PDF) 10 Page - STMicroelectronics