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EMC DESIGN GUIDE FOR ST MICROCONTROLLERS

3.1.3.2 Protective Interface

Although ST Microcontroller input/output circuitry has been designed taking ESD and Latch-

up problems into account, for those applications and systems where ST Microcontroller pins

are exposed to illegal voltages and high current injections, the user is strongly recommended

to implement hardware solutions which reduce the risk of damage: low-pass filters and clamp

diodes are usually sufficient in preventing stress conditions.

The risk of having out-of-range voltages and currents is greater for those signals coming from

outside the system, where noise effect or uncontrolled spikes could occur with higher proba-

bility than for the internal signals; it must be underlined that in some cases, adoption of filters

or other dedicated interface circuitries might affect global microcontroller performance, in-

ducing undesired timing delays, and impacting the global system speed.

Figure 14. Digital Input/Output - Push-Pull

PIN

OUTPUT

BUFFER

P

N

P

N

N

INPUT

BUFFER

P

ESD PROTECTION

CIRCUITRY

PORT CIRCUITRY

I/O CIRCUITRY

P

EN

EN