ST72321 datasheet(154/185 Pages) STMICROELECTRONICS

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ST72321

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EMC CHARACTERISTICS (Cont’d)

12.7.3.2 Static and Dynamic Latch-Up

LU: 3 complementary static tests are required

on 10 parts to assess the latch-up performance.

A supply overvoltage (applied to each power

supply pin) and a current injection (applied to

each input, output and configurable I/O pin) are

performed on each sample. This test conforms

to the EIA/JESD 78 IC latch-up standard. For

details,

refer

the

AN1181

ST7

application note.

DLU: Electro-Static Discharges (one positive

then one negative test) are applied to each pin

of 3 samples when the micro is running to

assess the latch-up performance in dynamic

mode. Power supplies are set to the typical

values, the oscillator is connected as near as

possible to the pins of the micro and the

component is put in reset mode. This test

conforms to the IEC1000-4-2 and SAEJ1752/3

standards and is described in Figure 80. For

details,

refer

the

AN1181

ST7

application note.

12.7.3.3 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).

Electrical Sensitivities

Figure 80. Simplified Diagram of the ESD Generator for DLU

Notes:

1. Class description: A Class is an STMicroelectronics internal specification. All its limits are higher than the JEDEC spec-

ifications, that means when a device belongs to Class A it exceeds the JEDEC standard. B Class strictly covers all the

JEDEC criteria (international standard).

2. Schaffner NSG435 with a pointed test finger.

Symbol

Parameter

Conditions

Class 1)

Static latch-up class

TA=+25°C

TA=+85°C

TA=+125°C

DLU

Dynamic latch-up class

VDD=5.5V, fOSC=4MHz, TA=+25°C

RCH=50MΩ

RD=330Ω

CS=150pF

ESD

HV RELAY

DISCHARGE TIP

DISCHARGE

RETURN CONNECTION

GENERATOR 2)

ST7

VDD

VSS

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