AN2482 Datasheet, PDF (4/18 Pages) STMicroelectronics – The purpose of this document

PCLT Description
AN2482
1.3
External biasing resistor settings
The PCLT operation mode can be set to the various logic input types defined by the
IEC 61131-2 standard. The current reference of the input-limiting block of each channel is
programmable by means of an external resistor R_REF. Moreover, because the operating
current range is different for each type, the external input resistor R_I can be changed to
improve the over-voltage robustness of the whole circuit. Table 1. defines the setting
resistances for the types 1, 2, and 3 and the corresponding performances of the PCLT input
and Figure 3. shows the current limiter variation versus the R_REF biasing resistor.
Table 1. Setting table
Type
1
3
2
Setting
Unit
R_REF
R_I
R_C
KΩ
22
10
KΩ
2.2
1.2
0.75
KΩ
2.2
Performances
I_{IN MIN}
mA
I_{IN TYP}
mA
I_{IN MAX}
mA
I_{LED TYP}
mA
Surge with R_I
kV
ESD with R_I
kV
2.2
6
3
7.1
4
8.5
1.9
4
1
0.5
8 in contact, 15 in air (class4)
Figure 3. Typical current limiter variation versus reference resistance R_REF
I_LIM / I_LIM (10 kΩ)
1.3
1.2
1.1
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
5.0E+00
1.0E+01
1.5E+01
2.0E+01
R_REF (kΩ)
2.5E+01
3.0E+01
4/18