CLT3-4B Datasheet, PDF (5/13 Pages) STMicroelectronics – Current limited over-voltage protected quad digital termination

CLT3-4B
Characteristics
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: the overall
module requires less cooling capability and becomes smaller.
The output block of each termination channel controls the operation of an opto-coupler that
is enabled by a Light Emitting Diode.
When the input current is less than 1.5 mA, this output circuit derivates the input current to
maintain the opto-coupler off.
The original structure of the CLT limiter allows its activation threshold to be low and
insensitive to the output voltage up to a maximum value of 2.0 V.
When the CLT input voltage V_IN is higher than 5 V, or the module input voltage Vi higher
than 11 V and a series resistor R_I = 1.2 kΩ, the output current that is a share of the input
current (3/4) is higher than 1.5 mA. The whole termination channel including the opto-
coupler is on.
Depending on the input type operation that is described by the IEC 61131-2 standard, the
input resistance R_I can be adjusted because of the different on-state threshold V_{ON MIN}.
This document describes operation and characteristics for type 3 operation with
V_{ON MIN} = 11 V and R_I = 1.2 kΩ.
In type 1 operation the on state threshold V_{ON MIN} is 12.34 V instead, and the input resistor
R_I is set 2.2 kΩ.
1.2
Input characteristics of CLT3-4
Figure 4. Typical input characteristics of each CLT3-4 channel
V_IN(V)
30
30
25
3.7
20
15
10
5
5
Off-state
On-state
0
0
0.5
1
1.5
2
2.5
3
3.5
4
I_IN(mA)
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