Description

AN3031

8/28

Doc ID 16144 Rev 1

2.2

STEVAL-IFP007V1 demonstration board

The STEVAL-IFP007V1 connection diagram is provided in Figure 4, 5 and 6. It is compliant

with type 1 and 3 input characteristics in accordance with the IEC 61131-2 standard. The

application is typically supplied from two sides using two independent power supplies -

primary and secondary. The primary power supply has a typical voltage of 24 VDC

(functional range from 16 to 35 VDC), and is connected to the CN9 terminal. The secondary

supply is connected through the CN10 (SPI) socket. This supply voltage level derives from

the microcontroller or control logic supply voltage. It is considered within range from 3 VDC

up to 5 VDC. For immunity considerations, the board design is optimized for 5 V signal

levels. If interconnection of the board with 3 V or 3.3 V logic is required, resistors R48, R49,

R59 and R60 should be replaced by a value of approximately 160

Ω.

dramatically influences the application’s EMC - high voltage surge robustness (IEC 61000-

4-5). The resistors should be capable of sustaining high peak voltage and current levels. A

resistors are 70 W, or 3 kV. Standard SMD 1206 resistors are not recommended, as their

rating are much lower. Therefore, the application fails at surge levels close to 1 kV

(differential mode, 42

Ω / 0.5 µF coupling).

Each SCLT3-8BT8 input signal is additionally filtered with a capacitor of 1 nF. These

components increase capacitive coupling to the GND reference and therefore maximize

EFT immunity. The capacitor values can be increased to 22 nF, for example, to achieve even

higher immunity levels, but with the drawback of bandwidth limitation.

Each SPI signal (CS, SCK, and MOSI) is filtered close to each SCLT3-8BT8 chip with an

integration R-C cell which limits the bandwidth to suppress noise sensitivity. Values used in

the application are 220

Ω - 100 pF, which correspond to the maximum communication baud

rate of approximately 3 Mbps. It is up to the application designer to set the appropriate R-C

values in order to suppress high frequency noise. Naturally, increasing the capacitor values

renders the signals more stable, which has a positive effect on the immunity, but the

communication bandwidth is lower.