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Capacitor Selection

Electrostatic Discharge (ESD) Protection

ESD Test Conditions

Human-Body Model (HBM)

−

+

DUT

1.5 k

Ω

100 pF

TRS211

5-V MULTICHANNEL RS-232 LINE DRIVER/RECEIVER

WITH

±15-kV ESD PROTECTION

SLLS811 – JULY 2007

APPLICATION INFORMATION (continued)

The capacitor type used for C1–C4 is not critical for proper operation. The TRS211 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, make sure 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,

influences the amount of ripple on V+ and V–.

Use larger capacitors (up to 10

μF) to reduce the output impedance at V+ and V–.

capacitors (C1–C4).

TI TRS211 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 testing is stringently performed by TI, based on various conditions and procedures. Please contact TI for a

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

The HBM of ESD testing is shown in Figure 7. Figure 8 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.

Figure 7. HBM ESD Test Circuit

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