+3V to +5.5V RS-232 Transceivers
with AutoShutdown
MAX3221/MAX3223/MAX3243
Pin Description
PIN
NAME
FUNCTION
MAX3221
MAX3223
MAX3243
Receiver Enable Control. Drive low for normal operation. Drive high to force
the receiver outputs into a high-Z state.
1
1
—
EN
5
6
5
6
1
2
C2+
C2-
Positive terminal of inverting charge-pump capacitor
Negative terminal of inverting charge-pump capacitor
-5.5V generated by the charge pump
RS-232 Receiver Inputs
7
7
3
V-
8
9, 16
8, 17
12, 13
10, 15
—
4–8
R_IN
13
11
9
9, 10, 11
12, 13, 14
15–19
20
T_OUT
T_IN
RS-232 Transmitter Outputs
TTL/CMOS Transmitter Inputs
R_OUT
R2OUTB
TTL/CMOS Receiver Outputs
—
Noninverting Receiver Output—active in shutdown
Output of the valid signal detector. Indicates if a valid RS-232 level is pres-
ent on receiver inputs logic “1”.
10
16
12
11
20
14
21
22
23
INVALID
FORCEOFF
FORCEON
Drive low to shut down transmitters and on-board power supply. This over-
rides all automatic circuitry and FORCEON (Table 1).
Drive high to override automatic circuitry keeping transmitters on
(FORCEOFF must be high) (Table 1).
4
14
15
3
4
18
19
3
24
25
26
27
28
C1-
Negative terminal of the voltage doubler charge-pump capacitor
Ground
GND
V
CC
+3.0V to +5.5V Supply Voltage
V+
+5.5V generated by the charge pump
Positive terminal of the voltage doubler charge-pump capacitor
2
2
C1+
RS-232 Transmitters
Detailed Description
The transmitters are inverting level translators that con-
vert CMOS-logic levels to 5.0V EIA/TIA-232 levels. They
Dual Charge-Pump Voltage Converter
The MAX3221/MAX3223/MAX3243’s internal power
supply consists of a regulated dual charge pump that
provides output voltages of +5.5V (doubling charge
pump) and -5.5V (inverting charge pump), regardless
guarantee a 120kbps data rate with worst-case loads of
3kΩ in parallel with 1000pF, providing compatibility with
PC-to-PC communication software (such as Laplink™).
Typically, the MAX3221/MAX3223/MAX3243 can oper-
ate at data rates of 235kbps. Transmitters can be paral-
leled to drive multiple receivers or mice (MAX3243).
Figure 1 shows a complete system connection.
of the input voltage (V ) over the +3.0V to +5.5V
CC
range. The charge pumps operate in a discontinuous
mode: if the output voltages are less than 5.5V, the
charge pumps are enabled; if the output voltages
exceed 5.5V, the charge pumps are disabled. Each
charge pump requires a flying capacitor (C1, C2) and
a reservoir capacitor (C3, C4) to generate the V+ and
V- supplies.
When FORCEOFF is driven to ground, or the Auto-
Shutdown circuitry senses invalid voltage levels at all
receiver inputs, the transmitters are disabled and the
outputs are forced into a high-impedance state.
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