1µA Supply-Current, True +3V to +5.5V
RS-232 Transceivers with AutoShutdown
______________________________________________________________Pin Description
PIN
MAX3221
1
5
6
7
8
13
11
9
—
10
16
12
4
14
15
3
2
MAX3223
1
5
6
7
9, 16
8, 17
12, 13
10, 15
—
11
20
14
4
18
19
3
2
MAX3243
—
1
2
3
4–8
9, 10, 11
12, 13, 14
15–19
20
21
22
23
24
25
26
27
28
NAME
EN
C2+
C2-
V-
R_IN
T_OUT
T_IN
R_OUT
R2OUTB
INVALID
FORCEOFF
FORCEON
C1-
GND
V
CC
V+
C1+
FUNCTION
Receiver Enable Control. Drive low for normal operation. Drive high to force
the receiver outputs into a high-Z state.
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
RS-232 Transmitter Outputs
TTL/CMOS Transmitter Inputs
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”.
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).
Negative terminal of the voltage doubler charge-pump capacitor
Ground
+3.0V to +5.5V Supply Voltage
+5.5V generated by the charge pump
Positive terminal of the voltage doubler charge-pump capacitor
MAX3221/MAX3223/MAX3243
_______________Detailed Description
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
of the input voltage (V
CC
) over the +3.0V to +5.5V
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.
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 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.
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.
LapLink is a trademark of Traveling Software.
_______________________________________________________________________________________
5
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