STR71XF_08 datasheet(47/78 Pages) STMICROELECTRONICS

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STR71xF

Electrical parameters

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4.3.4

EMC characteristics

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

Functional EMS (electro magnetic susceptibility)

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

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

LEDs).

●

ESD: Electro-Static 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.

●

FTB: A Burst of Fast Transient voltage (positive and negative) is applied to VDD and

VSS through a 100pF capacitor, until a functional disturbance occurs. This test

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).

In the case of an ARM7 CPU, in order to write robust code that can withstand all kinds of

stress, such as very strong electromagnetic disturbance, it is mandatory that the Data Abort,

Prefetch Abort and Undefined Instruction exceptions are managed by the application

software. This will prevent the code going into an undefined state or performing any

unexpected operation.

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