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
HUMANBODYMODELCURRENTWAVEFORM
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.
