Digital I/O design for industrial PLC

Digital-I/O solution with TLP2363, a photocoupler of 15Mbps high-speed communication
Digital I/O design for industrial PLC

Factory Automation (FA) is becoming an essential part of today's advanced manufacturing. The PLC (Programmable Logic Controller) plays a central role in realizing FA, and IEC 61131-2 *Note1 has been applying to the digital input module supporting PLC’s full input/output functions. Standardization have been developed for industrial control equipment since wide variety machines are interconnected, even in Japan, JIS B 3502 is specified for the PLC considered the use in an industrial environment. This time, we introduce the photocoupler TLP2363 for high-speed communication that is suitable for the design of digital input modules of PLC to meet the specification of IEC 61131-2.

[Note 1] IEC 61131-2: Requirements and Tests for Programmable Controller Equipment

TLP2363 Features

  1. Guarantees maximum and minimum threshold input currents
  2. High immunity to slow rise and fall of input and power supply

 

Guarantees maximum and minimum threshold input currents

IEC 61131-2 specifies three voltage/current operating ranges (types 1, 2, and 3) for the digital input modules used in the PLC. In the case of TLP2363, type 1 of voltage/current operating range can be applied by following the circuit constants described below. As shown in Fig. 1, the feature of requirement for digital input is that it defines the area that the module should be turned off. 

Fig. IEC 61131-2 Type 1 voltage/current operating area
Fig. IEC 61131-2 Type 1 voltage/current operating area

The configuration of the digital input module is shown in Figure 2. R1 and R2 must be configured to follow the operating area shown in Fig. 1. In conventional high-speed communication photocouplers, only the maximum value is guaranteed for the threshold input current that controls the high/low output, making it difficult to design a module that conforms to the operating area shown in Fig. 1.

Figure 2 Configuration of Digital Input Module
Figure 2 Configuration of Digital Input Module

TLP2363 ensures not only the maximum threshold input current but also the minimum value, which contributes to simplifying the design of the input module according to the operating area shown in Fig. 1.

In Fig. 2, by using peripheral components with following constants, the operating area shown in Fig. 1 can be covered under the ambient temperature -40°C to 105°C that TLP2363 ensure the operation. [Note2]

  • R1 = 2200 Ω
  • R2 = 750 Ω
  • RL = 1000 Ω
  • VCC = 3.3 V

[Note 2] Compliance is not guaranteed. Use this as a reference for the design policy.

High immunity to slow rise and fall of input and power supply

In addition to the above requirements for the operating area of the input circuit, IEC 61131-2 provides provisions for studies to be performed on the behavior of the PLC system with respect to variations in the external supply power. The gradual shutdown and start-up test of the external power supply is required to confirm that the specified behaviors are shown in advance when the power supply is turned on or off for 60 s.

TLP2363 does not need the Schmitt trigger shown in Fig. 2 (Fig. 4) because the output is stable without chattering even when the power supply is turned on or off for 60 s (Fig. 3). This contributes to reducing the number of component parts.

Fig. 3

Fig. 3   Left: VO behavior when starting VCC from 0V to 3.3V for 60 s
Right: VO behavior when VCC falls from 3.3V to 0V for 60 s
IF: Current flowing on the primary side (LEDs) of the photo coupler
VO: Output voltage

Fig. 4 Digital-input-module configuration using TLP2363
Fig. 4 Digital-input-module configuration using TLP2363

In addition, TLP2363 has a high tolerance against gradual rise and fall of the input signal so that stable output can be maintained even when the external input is unstable. (Fig. 5)

Fig. 5

Fig. 5 Left: VO behavior when starting IF from 0mA to 2.4mA for 60 s
Right: VO behavior when falling IF from 2.4mA to 0mA for 60 s
IF: Current flowing on the primary side (LEDs) of the photo coupler
VO: Output voltage

Since TLP2363 is an open-collector output type, the output logic is as follows when a voltage higher than the minimum operating voltage is applied to VCC.

Output Logic

LED

VO

ON

L

OFF

H

From the above, TLP2363 having 15 Mbps (typical) data transmission is suitable for the design of digital input modules of PLC that require high-speed I/O.

Part Number

TLP2363
StockChecking

Datasheet

PDF

Package
(Width×Length×Height mm)

5pin SO6
(3.7×7.0×2.1)

5pin SO6

Absolute Maximum Ratings

Operating temperature
Topr (℃)

-40 to 105

Output current
IO (mA)

25

Electrical Characteristics

Supply current
ICCH, ICCL max (mA)

4

Threshold input current (H/L)
IFHL (mA)

@VCC=3.3V, RL=1kΩ

0.3 to 2.4

Switching Characteristics

Propagation delay time
tpHL, tpLH max (ns)

80

Common-mode
transient immunity
CMH, CML min (kV/μs)
@Ta=25℃

±20

Isolation Characteristics

Isolation voltage
BVS min (Vrms)

@Ta=25℃

3750