ST72321 datasheet(153/189 Pages) STMICROELECTRONICS

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ST72321

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12.7 EMC CHARACTERISTICS

Susceptibility tests are performed on a sample ba-

sis during product characterization.

12.7.1

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 re-

sumed. The test results are given in the table be-

low based on the EMS levels and classes defined

in application note AN1709.

12.7.1.1 Designing hardened software to avoid

noise problems

EMC characterization and optimization are per-

formed at component level with a typical applica-

tion 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 manage-

ment 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 repro-

duced by manually forcing a low state on the RE-

SET pin or the Oscillator pins for 1 second.

To complete these trials, ESD stress can be ap-

plied directly on the device, over the range of

specification values. When unexpected behaviour

is detected, the software can be hardened to pre-

vent unrecoverable errors occurring (see applica-

tion note AN1015)

Symbol

Parameter

Conditions

Level/

Class

VFESD

Voltage limits to be applied on any I/O pin to induce a

functional disturbance

Flash device: VDD=5V, TA=+25°C,

fOSC=8MHz conforms to IEC 1000-4-2

ROM device: VDD=5V, TA=+25°C, fOSC=8

MHz, conforms to IEC 1000-4-2

VFFTB

Fast transient voltage burst limits to be applied

through 100pF on VDD and VDD pins to induce a func-

tional disturbance

VDD=5V, TA=+25°C, fOSC=8 MHz, con-

forms to IEC 1000-4-4

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