3.0V to 5.5V, Low-Power, up to 1Mbps, True RS-232
Transceivers Using Four 0.1µF External Capacitors
MAX3222/MAX3232/MAX3237/MAX3241
V
CC
0.1µF
T1IN
5V/div
V
CC
C1+
C1
C1-
C2+
C2
C2-
V+
C3
T1OUT
5V/div
R1OUT
5V/div
MAX3222
MAX3232
MAX3237
MAX3241
V-
C4
5µs/div
V
CC
= 3.3V
T_ OUT
T_ IN
Figure 6. MAX3241 Loopback Test Result at 120kbps
R_ OUT
0V
V
CC
EN
*
R_ IN
5k
1000pF
T1IN
5V/div
SHDN
*
GND
T1OUT
5V/div
*
MAX3222/MAX3241 ONLY
R1OUT
5V/div
Figure 5. Loopback Test Circuit
V
CC
= 3.3V
2µs/div
High Data Rates
The MAX3222/MAX3232/MAX3241 maintain the RS-232
±5.0V minimum transmitter output voltage even at high
data rates. Figure 5 shows a transmitter loopback test
circuit. Figure 6 shows a loopback test result at
120kbps, and Figure 7 shows the same test at 235kbps.
For Figure 6, all transmitters were driven simultaneously
at 120kbps into RS-232 loads in parallel with 1000pF.
For Figure 7, a single transmitter was driven at 235kbps,
and all transmitters were loaded with an RS-232 receiver
in parallel with 1000pF.
The MAX3237 maintains the RS-232 ±5.0V minimum
transmitter output voltage at data rates up to 1Mbps.
Figure 8 shows a loopback test result at 1Mbps with
MBAUD = V
CC
. For Figure 8, all transmitters were
loaded with an RS-232 receiver in parallel with 250pF.
Figure 7. MAX3241 Loopback Test Result at 235kbps
+5V
0V
+5V
0V
-5V
+5V
0V
R_OUT
150pF
200ns/div
V
CC
= 3.3V
T_OUT = R_IN
5k + 250pF
T_IN
Figure 8. MAX3237 Loopback Test Result at 1000kbps
(MBAUD = V
CC
)
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11
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
