±15kV ESD-Protected, 1µA, 3.0V to 5.5V, 250kbps,

RS-232 Transceivers with AutoShutdown

______________________________________________________________________________________

11

Level 4 (the highest level) of IEC1000-4-2, without the

need for additional ESD-protection components.

The major 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 model. Hence, the ESD with-

stand voltage measured to IEC1000-4-2 is generally

lower than that measured using the Human Body

Model. Figure 7a shows the IEEE1000-4-2 model and

Figure 7b 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

charged probe. The contact-discharge method connects

the probe to the device before the probe is energized.

Machine Model

The Machine Model for ESD tests all pins using a 200pF

storage capacitor and zero discharge resistance. Its

objective is to emulate the stress caused by contact that

occurs with handling and assembly during manufactur-

ing. Of course, all pins require this protection during

manufacturing, not just RS-232 inputs and outputs.

Therefore, after PC board assembly, the Machine Model

is less relevant to I/O ports.

___________Applications Information

Capacitor Selection

The capacitor type used for C1–C4 is not critical for

proper operation; either polarized or nonpolarized

capacitors may be used. The charge pump requires

0.1µF capacitors for 3.3V operation. For other supply

voltages, refer to Table 3 for required capacitor values.

Do not use values smaller than those listed in Table 3.

Increasing the capacitor values (e.g., by a factor of 2)

reduces ripple on the transmitter outputs and slightly

reduces power consumption. C2, C3, and C4 can be

increased without changing C1’s value. However, do

not increase C1 without also increasing the values of

C2, C3, and C4 to maintain the proper ratios (C1 to

the other capacitors).

CHARGE-CURRENT

LIMIT RESISTOR

DISCHARGE

RESISTANCE

STORAGE

CAPACITOR

Cs

100pF

HIGH-

VOLTAGE

DC

SOURCE

DEVICE

UNDER

TEST

CHARGE CURRENT

LIMIT RESISTOR

DISCHARGE

RESISTANCE

STORAGE

CAPACITOR

Cs

150pF

HIGH-

VOLTAGE

DC

SOURCE

DEVICE

UNDER

TEST

Figure 7a. IEC1000-4-2 ESD Test Model

tr = 0.7ns to 1ns

30ns

60ns

t

100%

90%

10%

I

Figure 7b. IEC1000-4-2 ESD Generator Current Waveform

Figure 6a. Human Body ESD Test Models

90%

36.8%

TIME

CURRENT WAVEFORM

PEAK-TO-PEAK RINGING

(NOT DRAWN TO SCALE)

Ir

10%

0

0

AMPERES

Figure 6b. Human Body Model Current Waveform