Application note

ST3237EB

10/18

6

Application note

This application note describes the procedure for determining the susceptibility and the test

method to verify ST ESD advanced protection on RS-232 or RS485 I/O device.

Static electricity is defined as an electrical charge caused by an imbalance of electrons on

the surface of a material. This imbalance of electrons produces an electric field that can be

measured and that can influence other objects at a distance. Electrostatic discharge is

defined as the transfer of charge between bodies at different electrical potentials.

Electrostatic discharge (ESD) can change the electrical characteristics of a semiconductor

device, degrading or destroying it. Any input or output port (I/O) allows access

communication with other pieces of equipment by external connectors. These connectors

are directly linked by the I/O pins of RS-232 or RS485 interface. ST provides the E-series by

advanced high ESD protection structure. The protection functionality is tested in two

different conditions:

The first model is used to simulate the HUMAN BODY MODEL (HBM) event. A similar

discharge can occur from a charged conductive object, such as a metallic tool or fixture. The

model used to characterize this event is known as the machine model. A human body model

circuit and waveform is presented in figures below.

Figure 7.

Human body model circuit

Figure 8.

Human body model current waveform