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4.7

EMC characteristics

Susceptibility tests are performed on a sample basis during product characterization.

4.7.1

Functional EMS (electromagnetic susceptibility)

Based on a simple running application on the product (toggling 2 LEDs through I/O ports),

the product is stressed by two electromagnetic events until a failure occurs (indicated by the

LEDs).

●

ESD: electrostatic discharge (positive and negative) is applied on all pins of the device

until a functional disturbance occurs. This test conforms with the IEC 1000-4-2

standard.

●

conforms with the IEC 1000-4-4 standard.

A device reset allows normal operations to be resumed. The test results are given in the

table below based on the EMS levels and classes defined in application note AN1709.

Designing hardened software to avoid noise problems

EMC characterization and optimization are performed at component level with a typical

application environment and simplified MCU software. It should be noted that good EMC

performance is highly dependent on the user application and the software in particular.

Therefore it is recommended that the user applies EMC software optimization and

prequalification tests in relation with the EMC level requested for his application.

●

Software recommendations

The software flowchart must include the management of runaway conditions such as:

–

Corrupted program counter

–

Unexpected reset

–

Critical Data corruption (control registers...)

●

Prequalification trials

Most of the common failures (unexpected reset and program counter corruption) can

be reproduced by manually forcing a low state on the Reset pin or the Oscillator pins for

1 second.

To complete these trials, ESD stress can be applied directly on the device, over the

range of specification values. When unexpected behavior is detected, the software can

be hardened to prevent unrecoverable errors occurring (see application note AN1015).

Table 17.

EMS characteristics

Symbol

Parameter

Conditions

Level/

Class

Voltage limits to be applied on any I/O pin

to induce a functional disturbance

conforms to IEC 1000-4-2

2B

Fast transient voltage burst limits to be

pins to induce a functional disturbance

conforms to IEC 1000-4-4

4B