CLT3-4B datasheet(7/13 Pages) STMICROELECTRONICS

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CLT3-4B

Application information

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Application information

2.1

Application description

The CLT device is used between the input module and the opto-coupler of an I/O module. To

secure the coupler off state and the non-conduction of its diode, the maximum CLT output

current is 40 µA with R opto = 15 k

Ω. When the CLT input voltage VIN is higher than 5 V, a

minimum CLT output current of 1.5 mA will secure the opto-coupler on state.

The CLT limiter is insensitive to the output voltage up to 2.0V. Therefore, its output is able to

drive any state of the art opto-coupler. Some additional device can be added in series with

the opto-coupler if the output voltage remains within its functional limits.

A stand-alone sensor is normally connected on the CLT input. For a good off state control,

its quiescent current has to be less than 1.5 mA (EN60947-5-2 standard compatible)

keeping then the opto-coupler off thanks to the CLT device (IOUT < 40 µA). And its maximum

ON state voltage VS-ON will be lower than 8 V (EN60947-5-2 standard compatible)

corresponding to the difference between the minimum supply voltage (VCC MIN = 19.2 V)

and the maximum current limitation activation voltage:

VCC MIN = VS-ON + VI

VI = VIN + RI x IIN MAX

(VI = 11 V when VIN = 5 V, RI = 1.2 kΩ, IIN < 3.7 mA).

2.2

Input reverse polarity robustness

Each input of the CLT device may be biased to a reverse polarity. This case corresponds to

a connection mistake or a reverse biasing that is generated by the demagnetization of a

monitored inductive solenoid.

The involved input can withstand the reverse current up to 20 mA (in the configuration

shown in Figure 10) through its input protection diode while its opto-coupler remains OFF.

Such a case is not critical for the CLT3-4 itself, as it represents less than 15 mW per

disturbed input. But the input resistors should be designed with care regardless of their

thermal characteristics (refer to Application note AN2527).

When the reverse polarity operation is required in types 3 input mode, it is recommended to

increase the input resistance RI to 1.8 kΩ in order to reduce its dissipation and keep the

input current below its maximum allowed level (20 mA). The surge and transient immunity

robustness of the CLT3 is then also increased.

A 1.8 k

Ω value allows the reverse input current to be reduced to 16.2 mA and the resistor

dissipation to be reduced to 0.47 W, for 30 V VCC and a - 30 V VI voltages.

The CLT3 normal operation in type 3 is fully compatible with this recommended resistance

since its internal state threshold is monitored at VIN = 4.2 V and VC = 10V - corresponding to

VI = 11 V and VCC = 19 V.

In type 1 input operation where RI = 2.2 kΩ the dissipation of this resistor is less than

0.39 W.

The other inputs remain operational, as long as the power supply is working properly

(VCC >19 V). Refer to Application note AN 2527 for representative application design case.

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