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13

±15kV ESD-Protected, +5V RS-232 Transceivers

__________Applications Information

Capacitor Selection

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

proper operation. The MAX202E, MAX206–MAX208E,

MAX211E, and MAX213E require 0.1µF capacitors,

and the MAX232E and MAX241E require 1µF

capacitors, although in all cases capacitors up to 10µF

can be used without harm. Ceramic, aluminum-

electrolytic, or tantalum capacitors are suggested for

the 1µF capacitors, and ceramic dielectrics are

suggested for the 0.1µF 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., 2x) 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 10µF) to reduce the output

impedance at V+ and V-. This can be useful when

“stealing” power from V+ or from V-. The MAX203E and

MAX205E have internal charge-pump capacitors.

applications sensitive to power-supply noise generated

capacitor the same size as (or larger than) the charge-

pump capacitors (C1–C4).

V+ and V- as Power Supplies

A small amount of power can be drawn from V+ and V-,

although this will reduce both driver output swing and

noise margins. Increasing the value of the charge-pump

capacitors (up to 10µF) helps maintain performance

when power is drawn from V+ or V-.

Driving Multiple Receivers

Each transmitter is designed to drive a single receiver.

Transmitters can be paralleled to drive multiple

receivers.

Driver Outputs when Exiting Shutdown

The driver outputs display no ringing or undesirable

transients as they come out of shutdown.

High Data Rates

These transceivers maintain the RS-232 ±5.0V

minimum driver output voltages at data rates of over

120kbps. For data rates above 120kbps, refer to the

Transmitter Output Voltage vs. Load Capacitance

graphs in the Typical Operating Characteristics.

Communication at these high rates is easier if the

capacitive loads on the transmitters are small; i.e.,

short cables are best.

Table 2. Summary of EIA/TIA-232E, V.28 Specifications

PARAMETER

CONDITIONS

EIA/TIA-232E, V.28

SPECIFICATIONS

0 Level

3kΩ to 7kΩ load

+5V to +15V

Data Rate

Up to 20kbps

+3V to +15V

Instantaneous Slew Rate, Max

30V/µs

Driver Output Short-Circuit Current, Max

100mA

Transition Rate on Driver Output

V.28

1ms or 3% of the period

Driver Output Resistance

300Ω

EIA/TIA-232E

4% of the period

Driver Output Level, Max

No load

±25V

Driver Output Voltage

3kΩ to 7kΩ load

-5V to -15V

0 Level

1 Level

1 Level

Receiver Input Level

±25V

Receiver Input Voltage

-3V to -15V