±15kV ESD-Protected, 1µA, 3.0V to 5.5V, 250kbps,
RS-232 Transceivers with AutoShutdown
MAX3221E/MAX3223E/MAX3243E
Pin Description
PIN
MAX3221E
1
2
3
4
5
6
7
8
9
10
11
12
13
—
14
15
16
MAX3223E
1
2
3
4
5
6
7
9, 16
10, 15
11
12, 13
14
8, 17
—
18
19
20
MAX3243E
—
28
27
24
1
2
3
4–8
15–19
21
12, 13, 14
23
9, 10, 11
20
25
26
22
NAME
EN
C1+
V+
C1-
C2+
C2-
V-
R_IN
R_OUT
INVALID
T_IN
FORCEON
T_OUT
R2OUTB
GND
V
CC
FORCEOFF
FUNCTION
Receiver Enable Control. Drive low for normal operation. Drive high to
force the receiver outputs (R_OUT) into a high-impedance state.
Positive terminal of the voltage doubler Charge-Pump Capacitor
+5.5V generated by the charge pump
Negative terminal of the voltage doubler Charge-Pump Capacitor
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
TTL/CMOS Receiver Outputs
Output of the Valid Signal Detector.
INVALID
is enabled high if a valid
RS-232 level is present on any receiver input.
TTL/CMOS Transmitter Inputs
Drive high to override automatic circuitry keeping transmitters and
charge pump on (FORCEOFF must be high) (Table 1).
RS-232 Transmitter Outputs
TTL/CMOS Noninverting Complementary Receiver Output. Always
active.
Ground
+3.0V to +5.5V Supply Voltage
Force-Off Input, active low. Drive low to shut down transmitters,
receivers (MAX3243E, except R2OUTB), and on-board charge pump.
This overrides all automatic circuitry and FORCEON (Table 1).
_______________Detailed Description
Dual Charge-Pump Voltage Converter
The MAX3221E/MAX3223E/MAX3243E’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), over the
+3.0V to +5.5V V
CC
range. The charge pumps operate
in 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.
RS-232 Transmitters
The transmitters are inverting level translators that con-
vert CMOS-logic levels to 5.0V EIA/TIA-232 levels. They
guarantee a 250kbps data rate with worst-case loads
of 3kΩ in parallel with 1000pF, providing compatibility
with PC-to-PC communication software such as
LapLink™. Transmitters can be paralleled to drive mul-
tiple receivers. The MAX3243E has been specifically
designed to drive serial mice. Figure 1 shows a com-
plete system connection.
When
FORCEOFF
is driven to ground, or the
AutoShutdown circuitry senses invalid voltage levels on
all receiver inputs, the transmitters are disabled and the
outputs are forced into a high-impedance state. When
powered off or shut down, the output can be driven up
to ±12V. The transmitter inputs do not have pull-up
resistors.
LapLink is a trademark of Traveling Software.
6
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