Datasheet

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 V
CC
to ground with at least 0.1μF. In applications
sensitive to power-supply noise generated by the charge
pumps, decouple V
CC
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 ≤ R
L
≤ 7kΩ, C
L
≤ 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 ≤ R
L
≤ 7kΩ, C
L
≤ 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 < V
OUT
< +2V 300Ω
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MAX202E–MAX213E,
MAX232E/MAX241E
±15kV ESD-Protected,
5V RS-232 Transceivers