ST3237E

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Figure 3: LOW Level Receiver Output Current

Figure 4: HIGH Level Receiver Output Current

Figure 5: ESD Protection

Note: The High ESD protected pins are the I/O RS232 line, transmitter out and receiver in. The other pins guarantee ± 2KV HBM ESD pro-

tection versus ground by means of diodes.

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.