1ꢀ5k EꢁD-ꢂrotected, +ꢀk Rꢁ-232 Transceivers
k+ and k- as ꢂower ꢁupplies
A small amount of power can be drawn from V+ and V-,
__________Applications Inforꢃation
Capacitor ꢁelection
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, ma5e 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-.
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 ꢁhutdown
The driver outputs display no ringing or undesirable
transients as they come out of shutdown.
High Data Rates
These transceivers maintain the RS-232 ꢀ.0V
minimum driver output voltages at data rates of over
1205bps. For data rates above 1205bps, 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 smallꢁ i.e.,
short cables are best.
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
MAX20ꢀE have internal charge-pump capacitors.
Bypass V
to ground with at least 0.1µF. In
CC
applications sensitive to power-supply noise generated
by the charge pumps, decouple V to ground with a
CC
capacitor the same size as (or larger than) the charge-
pump capacitors (C1–C4).
Table 2. Summary of EIA/TIA-232E, V.28 Specifications
EIA/TIA-232E, V.28
SPECIFICATIONS
PARAMETER
CONDITIONS
35Ω to 75Ω load
0 Level
+ꢀV to +1ꢀV
Driver Output Voltage
1 Level
35Ω to 75Ω load
-ꢀV to -1ꢀV
2ꢀV
Driver Output Level, Max
Data Rate
No load
35Ω ≤ R ≤ 75Ω, C ≤ 2ꢀ00pF
Up to 205bps
+3V to +1ꢀV
-3V to -1ꢀV
2ꢀV
L
L
0 Level
1 Level
Receiver Input Voltage
Receiver Input Level
Instantaneous Slew Rate, Max
35Ω ≤ R ≤ 75Ω, C ≤ 2ꢀ00pF
30V/µs
L
L
Driver Output Short-Circuit Current, Max
100mA
V.28
EIA/TIA-232E
-2V < V < +2V
1ms or 3% of the period
4% of the period
300Ω
Transition Rate on Driver Output
Driver Output Resistance
OUT
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MAXIM [ MAXIM INTEGRATED PRODUCTS ]
