+5V, RS-232 Transceivers
with 0.1F External Capacitors
Applications Information
Capacitor Selection
The type of capacitor used is not critical for proper
operation. Ceramic capacitors are suggested. To ensure
proper RS-232 signal levels over temperature when
using 0.1FF capacitors, make sure the capacitance
value does not degrade excessively as the temperature
varies. If in doubt, use capacitors with a larger nominal
value. Also observe the capacitors’ ESR value over tem-
perature, since it influences the amount of ripple on V+
and V-. To reduce the output impedance at V+ and V-,
use larger capacitors (up to 10FF). If polarized capaci-
tors are used, obey the polarities shown in Figure 1 and
the pin configurations.
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
Figure 5 shows two driver outputs exiting shutdown. As
they become active, the two driver outputs go to oppo-
site RS-232 levels (one driver input is high, the other
is low). Each driver is loaded with 3kI in parallel with
2500pF. The driver outputs display no ringing or undesir-
able transients as they come out of shutdown.
Power-Supply Decoupling
In applications that are sensitive to power-supply noise,
decouple VCC to ground with a capacitor of the same
value as the charge-pump capacitors.
V+ and V- as Power Supplies
A small amount of power can be drawn from V+ and V-,
although this reduces noise margins.
Power Supplies for MAX201/MAX209
If at power-up the V+ supply rises after the VCC supply,
place a diode (e.g., 1N914) in series with the V+ supply.
Table 3. DB9 Cable Connections Commonly Used for EIA/TIA-232E and V.24
Asynchronous Interfaces
Table 2. Summary of EIA/TIA-232E, V.28 Specifications
PARAMETER
CONDITION
EIA/TIA-232E, V.28 SPECIFICATION
Driver Output Voltage: 0 Level
3kI to 7kI load
+5.0V to +15V
Driver Output Voltage: 1 Level
3kI to 7kI load
-5.0V to -15V
Output Level, Maximum
No load
Q
25V
Data Rate
3kI P RL P 7kI, CL P 2500pF
Up to 20kbps
Receiver Input Voltage: 0 Level
—
+3.0V to +15V
Receiver Input Voltage: 1 Level
—
-3.0V to -15V
Input Level, Maximum
—
Q
25V
Instantaneous Slew Rate, Maximum
3kI P RL P 7kI, CL P 2500pF
30V/Fs
Driver Output Short-Circuit Current, Maximum
—
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
300I
PIN
NAME
CONNECTION
1
Received Line Signal Detector, sometimes called Carrier Detect (DCD)
Handshake from DCE
2
Receive Data (RD)
Data from DCE
3
Transmit Data (TD)
Data from DTE
4
Data Terminal Ready
Handshake from DTE
5
Signal Ground
Reference point for signals
6
Data Set Ready (DSR)
Handshake from DCE
7
Request to Send (RTS)
Handshake from DTE
8
Clear to Send (CTS)
Handshake from DCE
9
Ring Indicator
Handshake from DCE
MAX200–MAX209/MAX211/MAX213
8
Maxim Integrated