ST3237E

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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.

HUMAN BODY MODEL CIRCUIT

HUMAN BODY MODEL CURRENT WAVEFORM

The second model is IEC 1000-4-2 and is used to simulate the reaction of the device on equipment when

subjected to electrostatic discharges, which may occur from personnel to objects near vital

instrumentation. Direct (Contact) and indirect (Air Gap) applications of discharges to the equipment under

test (EUT) are possible. Test characteristics are shown in circuit, waveform and table below.