MAX232ECSE datasheet(13/26 Pages) AD

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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 capaci-

tors. When using the minimum recommended capaci-

tor 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 out-

put 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.

Bypass VCC to ground with at least 0.1μF. In applications

sensitive to power-supply noise generated by the charge

pumps, decouple VCC to ground with a 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

Driver Output Voltage

0 Level

3kΩ to 7kΩ load

+5V to +15V

1 Level

3kΩ to 7kΩ load

-5V to -15V

Driver Output Level, Max

No load

±25V

Data Rate

3kΩ ≤ RL ≤ 7kΩ, CL ≤ 2500pF

Up to 20kbps

Receiver Input Voltage

0 Level

+3V to +15V

1 Level

-3V to -15V

Receiver Input Level

±25V

Instantaneous Slew Rate, Max

3kΩ ≤ RL ≤ 7kΩ, CL ≤ 2500pF

30V/μs

Driver Output Short-Circuit Current, Max

100mA

Transition Rate on Driver Output

V.28

1ms or 3% of the period

EIA/TIA-232E

4% of the period

Driver Output Resistance

-2V < VOUT < +2V

300Ω

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Analog Devices │ 13

MAX202E–MAX213E,

MAX232E/MAX241E

±15kV ESD-Protected,

5V RS-232 Transceivers

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