AN2846 datasheet(30/35 Pages) STMICROELECTRONICS

30 / 35 page

Electromagnetic compatibility (EMC) requirements

AN2846

30/35

Doc ID 15130 Rev 1

6.2

IEC 61000 4-4

This standard specifies the behavior of the device when subjected to a fast transient burst.

The fast transient burst must be applied on all the input pins of the system. A capacitive

clamp-coupling device is used as described in the IEC 61000-4-4 standard. The required

sustainable burst voltage level is 2.5 kV. The system must continue to operate as intended.

No temporary degradation of the performance is acceptable during the test (A criterion).

New test methodology has been set up to check the frame integrity against fast transient

bursts. The need to monitor each bit level leads to using a scope isolated from the test

bench through optic fibers. The generation of /CS and SCK input signals are also isolated

through the same way as shown in Figure 39. Current and voltage level adaptation is done

through an optical fiber interface (OFI).

Long frames history can be stored in the monitoring scope for an easier detection of

disrupted bits.

The SCLT3-8 immunity has been increased by adding RC filter networks connected on /CS

and SCK input pins. But these RC filters act as low pass filters and limit the maxim data

transfer speed. For example the filter made of R = 220

Ω, C = 470 pF allows a 1 MHz

transmission frequency and ensures device FTB immunity up to 4 kV.

The test configuration is shown in Figure 39.

Figure 39.

Two supplies configuration

Table 4.

Speed - FTB immunity compromise

RC Values

SCK speed

FTB immunity

220

Ω - 220 pF

2 MHz

3 kV

220

Ω – 470 pF

1 MHz

4 kV

Generator

Capacitive clamp

SCLT3-8

OFI

/CS

MISO

SCK

OFI

/CS

MISO

SCK

/CS

MISO

SCK

Scope

Fiber optic cable

FTB

generator

Bat

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