±15kV ESD-Protected, EMC-Compliant, 230kbps

RS-232 Serial Port for Modems

6

_______________________________________________________________________________________

Human Body Model

Figure 2a shows the Human Body Model, and Figure

2b shows the current waveform it generates when dis-

charged into a low impedance. This model consists of

a 100pF capacitor charged to the ESD voltage of inter-

est, which is then discharged into the device through a

1.5k

Ω resistor.

IEC1000-4-2

The IEC1000-4-2 standard covers ESD testing and per-

formance of finished equipment; it does not specifically

refer to integrated circuits. The MAX3186 helps you

design equipment that meets Level 4 (the highest level)

of IEC1000-4-2, without additional ESD-protection com-

ponents.

The main difference between tests done using the

Human Body Model and IEC1000-4-2 is higher peak

current in IEC1000-4-2. Because series resistance is

lower in the IEC1000-4-2 ESD test model (Figure 1a),

the ESD withstand voltage measured to this standard is

generally lower than measured using the Human Body

Model. Figure 1b shows the current waveform for the

±8kV IEC1000-4-2 Level 4 ESD Contact-Discharge test.

The Air-Gap test involves approaching the device with a

charge probe. The Contact-Discharge method connects

the probe to the device before the probe is energized.

Machine Model

The Machine Model for ESD testing uses a 200pF stor-

age capacitor and zero-discharge resistance. It mimics

the stress caused by handling during manufacturing

and assembly. Of course, all pins (not just RS-232

inputs and outputs) require this protection during man-

ufacturing. Therefore, the Machine Model is less rele-

vant to the I/O ports than are the Human Body Model

and IEC1000-4-2.

__________Applications Information

Use proper layout to ensure other devices on your

board are not damaged in an ESD strike. Currents as

high as 60A can instantaneously pass into the ground,

so be sure to minimize the ground-lead return path to

the power supply. A separate return path to the power

supply is recommend. Trace widths should be greater

capacitors as close to the part as possible to ensure

maximum ESD protection.

protection diodes are needed because the MAX3186 is

not sensitive to power-supply sequencing.

CHARGE-CURRENT

LIMIT RESISTOR

DISCHARGE

RESISTANCE

STORAGE

CAPACITOR

Cs

100pF

HIGH-

VOLTAGE

DC

SOURCE

DEVICE

UNDER

TEST

Figure 2a. Human Body ESD Test Model

90%

36.8%

TIME

CURRENT WAVEFORM

PEAK-TO-PEAK RINGING

(NOT DRAWN TO SCALE)

Ir

10%

0

0

AMPERES

Figure 2b. Human Body Model Current Waveform