AN2846

Application guidelines

Doc ID 15130 Rev 1

7/35

Figure 5.

Input characteristic according to IEC 61131-2 type 3

Current limited inputs allow reduced power dissipation into the device as well as reduced

power needed by the external supplies. A typical application circuit schematic is shown in

Figure 31 in the application section.

Figure 6 displays the SCLT3-8 input stage configuration and its typical input threshold

voltages. Low frequency triangular waveform as the input voltage has been used to better

Figure 6.

Input stage

and 8.5 V, consistent with the 11 V min. and 5 V max specified in the IEC 61131-2 standard.

The hysteresis (1 V) improves the input noise immunity.

is reached.

In all cases the following formula can be applied:

When the input current limiter is activated, the formula becomes:

The typical module input threshold voltage can be calculated as follow:

11V

5V

2.0

1.5

ON

OFF

ON

0.1

11V

5V

ON Region

OFF Region

Transition Region

SCLT3-8 (including R

input characteristic

OFF

OFF

LED

R

IN

V

I

INPUT STATUS

V

TH

I

IN

DIGITAL

FILTER

V

IN

: 2V/div

VI: 2V/div

I IN: 1mA/div

V

LED

I

Input stage configuration

Typical input voltage thresholds

IN

IN

IN

I

V

I

R

V+

×

=

IN

ILIM

IN

I

V

I

R

V+

×

=

Math Composer 1.1.5

ON

VTH

ILIM

IN

ON

IN

V

I

R

V

_

_

+

×

=