AN2846

Application circuit

Doc ID 15130 Rev 1

23/35

3.2

Component definitions

is suggested.

also achieved as shown in Table 3.

The input MELF resistors are used to sustain high voltages occurring during surge tests.

product of SCLT3-8 supply current and any load current supplied by VDD: regulator output

8 V activation threshold to avoid a spurious power loss detection. 1 k

Ω meets this

requirement and allows 2 kV of voltage surge.

The 22 nF input capacitors are used to improve the noise immunity of the whole module.

Their function is to filter the high frequency electrical noise, and to secure the off state of the

module.

that described in the IEC 61131-2 standard.

below 20 µs.

The LEDs must be chosen according to their input diode drop voltage. LED outputs can

drive LEDs with forward voltage up to 2.7 V.

Low pass RC filters have been inserted into digital inputs /CS and SCK to improve the

immunity against fast transient bursts. R = 220

Ω and C = 470 pF give a good compromise

between immunity result and SCLT-3 speed which can run up to 1 MHz.

Table 3.

Type 2 and 3 configurations

Type 3

Type 2

Unit

15

3.9

k

Ω

2.2

0.75

k

Ω

2.3

6.5

mA