MAX222

5V DUAL RS232 LINE DRIVER/RECEIVER

WITH ±15kV ESD PROTECTION

SLLS590D − SEPTEMBER 2003 − REVISED AUGUST 2004

8

POST OFFICE BOX 655303

APPLICATION INFORMATION

capacitor selection

The capacitor type used for C1−C4 is not critical for proper operation. The MAX222 requires 0.1-

µF capacitors,

although capacitors up to 10

µF can be used without harm. Ceramic dielectrics are suggested for the 0.1-µF

capacitors. When using the minimum recommended capacitor values, ensure that the capacitance value does

not degrade excessively as the operating temperature varies. If in doubt, use capacitors with a larger (e.g., 2

×)

nominal value. The capacitors’ effective series resistance (ESR), which usually rises at low temperatures,

Use larger capacitors (up to 10

capacitors (C1−C4).

ESD protection

TI MAX222 devices have standard ESD protection structures incorporated on the pins to protect against

electrostatic discharges encountered during assembly and handling. In addition, the RS232 bus pins (driver

outputs and receiver inputs) of these devices have an extra level of ESD protection. Advanced ESD structures

were designed to successfully protect these bus pins against ESD discharge of

±15-kV when powered down.

ESD test conditions

ESD testing stringently is performed by TI, based on various conditions and procedures. Contact TI for a

reliability report that documents test setup, methodology, and results.

Human-Body Model

The Human-Body Model (HBM) of ESD testing is shown in Figure 5, while Figure 6 shows the current waveform

that is generated during a discharge into a low impedance. The model consists of a 100-pF capacitor, charged

to the ESD voltage of concern, and subsequently discharged into the DUT through a 1.5-k

Ω resistor.

−

+

DUT

RD

1.5 k

Ω

VHBM

100 pF

CS

Figure 5. HBM ESD Test Circuit