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ST termination device improves reliability of 24V DC input modules

Posted: 23 Jun 2006     Print Version  Bookmark and Share

Keywords:STMicroelectronics  termination  24V DC input module  PCLT-2AT4  industrial automation 

ST's termination device

STMicroelectronics has introduced a dual termination device that promises to improve the performance and reliability of 24V DC digital input modules used in industrial automation systems. The device integrates input voltage protection, a serial current limiter and an output driver.

According to ST, the PCLT-2AT4, which comes in a small TSSOP14 surface mount package, reduces considerably the cost and the board space required by traditional discrete component solutions, while dramatically cutting power losses and providing better EMI immunity. Each of the two channels terminates the connection between a high-side proximity sensor and the input of the I/O module, and the compact device offers a flexible and easy-to-design solution for the production of highly integrated 24V interfaces, the company said.

The device is a flexible solution to achieve Type 1, Type 2 and Type 3 characteristics of the IEC61131-2 standard, ST said, which defines equipment requirements and tests for industrial programmable logic controllers. The current limit is programmable with a single external resistor to between 7.5mA (Type 2) and 2.5mA (Type 3), and temperature compensation over the operating temperature range further reduces dissipation compared to resistive circuitry. In addition, the low thermal resistance of the exposed pad package allows the PCB cooling pad to be smaller and reduces the hot spot effect, the company explained.

The outputs can be configured as opto-coupler drivers, or as CMOS outputs to drive a bus controller directly, under single input control. Outputs are disabled in both modes when the input current is less than 2mA, in accordance with IEC61131-2. In addition, an LED driver is powered by the input current, providing visual indication of the input logic state.

Input voltage clamping protects the module inputs against EMI as defined in IEC61131-2, and in IEC61000-4-2 (1.5kV air ESD), IEC61000-4-4 (4kV fast transient burst), and IEC61000-4-6-5 (0.5- to 1kV voltage surge). The inputs are protected against -30V steady state reverse polarity. With a 750 ohmΩ series resistor, the operating input voltage range is a wide -30V to 35V.

The PCLT-2AT4 joins ST's existing CLT3-4BT6 quad termination, which is designed to meet the IEC61131-2 Type 3 characteristic. This device is available in sample quantities. US pricing is Rs.32.08 (70 cents) each for 1,000 units.

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